diff --git a/viewer/CMakeLists.txt b/viewer/CMakeLists.txt
index cc5ef09b8..e11938c98 100644
--- a/viewer/CMakeLists.txt
+++ b/viewer/CMakeLists.txt
@@ -56,6 +56,8 @@ ADD_EXECUTABLE(jfjoch_viewer jfjoch_viewer.cpp JFJochViewerWindow.cpp JFJochView
         windows/JFJochViewerImageListWindow.h
         widgets/NumericComboBox.cpp
         widgets/NumericComboBox.h
+        widgets/LiveComboBox.cpp
+        widgets/LiveComboBox.h
         windows/JFJochViewerMetadataWindow.cpp
         windows/JFJochViewerMetadataWindow.h
         windows/JFJochMergeStatsWindow.cpp
diff --git a/viewer/JFJochViewerDatasetInfo.cpp b/viewer/JFJochViewerDatasetInfo.cpp
index dc5757683..4ffed3d36 100644
--- a/viewer/JFJochViewerDatasetInfo.cpp
+++ b/viewer/JFJochViewerDatasetInfo.cpp
@@ -40,7 +40,7 @@ namespace {
 
 JFJochViewerDatasetInfo::JFJochViewerDatasetInfo(QWidget *parent) : QWidget(parent) {
     auto layout = new QGridLayout(this);
-    combo_box = new QComboBox(this);
+    combo_box = new LiveComboBox(this);
 
     layout->addWidget(combo_box, 0, 0);
 
@@ -117,6 +117,16 @@ JFJochViewerDatasetInfo::JFJochViewerDatasetInfo(QWidget *parent) : QWidget(pare
         SaveFavourite();
     });
 
+    // Items held back while the dropdown was open went in once it closed: re-apply the selection
+    // rules and re-plot, as after any other rebuild.
+    connect(combo_box, &LiveComboBox::itemsReplaced, this, [this] {
+        RestoreSelection();
+        if (combo_is_image_mode_)
+            comboBoxSelected(combo_box->currentIndex());
+        else
+            UpdatePlot();
+    });
+
     connect(grid_scan_image, &JFJochGridScanImage::imageSelected,
             this, &JFJochViewerDatasetInfo::imageSelectedInChart);
 
@@ -249,32 +259,32 @@ void JFJochViewerDatasetInfo::changeEvent(QEvent *event) {
 }
 
 void JFJochViewerDatasetInfo::UpdateLabels() {
-    QSignalBlocker bl(combo_box);
-
     if (combo_box->count() > 0)
         (combo_is_image_mode_ ? last_image_selection : last_selection) = combo_box->currentData().toInt();
 
-    combo_box->clear();
     combo_is_image_mode_ = image_button && image_button->isChecked();
 
+    // Built in full and handed over as one list: the combo only changes when the list does, so the
+    // live updates that call this on every tick leave an open dropdown and the selection alone.
+    QVector<LiveComboBox::Item> items;
+    auto add = [&items](const QString &text, int code) { items.push_back({text, code}); };
+    auto separator = [&items] { items.push_back({.separator = true}); };
+
     // In per-image mode the one combo selects which per-image profile to show (no second combo).
     if (combo_is_image_mode_) {
         for (const auto &pt : JFJochViewerSidePanelChart::PlotTypes())
-            combo_box->addItem(pt.first, pt.second);
-        return;
-    }
-
-    if (this->dataset) {
-        combo_box->addItem("Background estimate", 0);
+            add(pt.first, pt.second);
+    } else if (this->dataset) {
+        add("Background estimate", 0);
         if (!dataset->experiment.GetGridScan().has_value())
-            combo_box->addItem("Spots + background", SPOTS_PLUS_BACKGROUND);
-        combo_box->addItem("Ice ring score", 14);
-        combo_box->addItem("Spindle blind fraction", 15);
-        combo_box->addItem("Resolution estimate", 7);
-        combo_box->addItem("Spot count", 1);
-        combo_box->addItem("Spot count (indexed)", 2);
-        combo_box->addItem("Spot count (ice rings)", 3);
-        combo_box->addItem("Spot count (low res.)", 4);
+            add("Spots + background", SPOTS_PLUS_BACKGROUND);
+        add("Ice ring score", 14);
+        add("Spindle blind fraction", 15);
+        add("Resolution estimate", 7);
+        add("Spot count", 1);
+        add("Spot count (indexed)", 2);
+        add("Spot count (ice rings)", 3);
+        add("Spot count (low res.)", 4);
 
         // Offer indexing/scaling metrics if the active run, any overlay run, or the live run has them.
         bool has_indexing = !dataset->indexing_result.empty();
@@ -290,31 +300,30 @@ void JFJochViewerDatasetInfo::UpdateLabels() {
         }
 
         if (has_indexing) {
-            combo_box->insertSeparator(1000);
-            combo_box->addItem("Indexing result", 5);
-            combo_box->addItem("Profile radius", 6);
-            combo_box->addItem("B-factor", 8);
-            combo_box->addItem("Mosaicity", 9);
-            combo_box->addItem("Integrated reflections", 12);
-            combo_box->addItem("Indexing lattice count", 13);
+            separator();
+            add("Indexing result", 5);
+            add("Profile radius", 6);
+            add("B-factor", 8);
+            add("Mosaicity", 9);
+            add("Integrated reflections", 12);
+            add("Indexing lattice count", 13);
         }
 
         if (has_scale) {
-            combo_box->insertSeparator(1000);
-            combo_box->addItem("Scale factor", 10);
-            combo_box->addItem("CC", 11);
+            separator();
+            add("Scale factor", 10);
+            add("CC", 11);
         }
         for (int i = 0; i < this->dataset->roi.size(); i++) {
-            std::string name = std::string("ROI ") + this->dataset->roi[i];
-            combo_box->insertSeparator(1000);
-            combo_box->addItem(QString::fromStdString(name + " mean"), 100 + i * 4);
-            combo_box->addItem(QString::fromStdString(name + " sum"), 100 + i * 4 + 1);
-            combo_box->addItem(QString::fromStdString(name + " weighted x"), 100 + i * 4 + 2);
-            combo_box->addItem(QString::fromStdString(name + " weighted y"), 100 + i * 4 + 3);
+            const QString name = QString::fromStdString("ROI " + this->dataset->roi[i]);
+            separator();
+            add(name + " mean", 100 + i * 4);
+            add(name + " sum", 100 + i * 4 + 1);
+            add(name + " weighted x", 100 + i * 4 + 2);
+            add(name + " weighted y", 100 + i * 4 + 3);
         }
-    } else {
-        combo_box->clear();
     }
+    combo_box->SetItems(items);
 }
 
 
diff --git a/viewer/JFJochViewerDatasetInfo.h b/viewer/JFJochViewerDatasetInfo.h
index 0397aeeaf..3cedce864 100644
--- a/viewer/JFJochViewerDatasetInfo.h
+++ b/viewer/JFJochViewerDatasetInfo.h
@@ -14,10 +14,11 @@
 #include "image_viewer/JFJochGridScanImage.h"
 #include "widgets/JFJochViewerSidePanelChart.h"
 #include "RunData.h"
+#include "widgets/LiveComboBox.h"
 
 class JFJochViewerDatasetInfo : public QWidget {
     Q_OBJECT
-    QComboBox *combo_box;
+    LiveComboBox *combo_box;
     JFJochDatasetInfoChartView *chart_view;
     // Second half-height plot under the first, shown only for "Spots + background": the spot
     // count and the background each get their own compact plot instead of sharing twin axes.
diff --git a/viewer/widgets/JFJochViewerROIList.cpp b/viewer/widgets/JFJochViewerROIList.cpp
index 78800a731..ab4a701b3 100644
--- a/viewer/widgets/JFJochViewerROIList.cpp
+++ b/viewer/widgets/JFJochViewerROIList.cpp
@@ -14,15 +14,14 @@
 #include <QGridLayout>
 #include <QPushButton>
 #include <QInputDialog>
-#include <QPixmap>
-#include <QIcon>
 
 JFJochViewerROIList::JFJochViewerROIList(QWidget *parent) : QWidget(parent) {
     auto *layout = new QVBoxLayout(this);
 
-    combo_ = new QComboBox(this);
+    combo_ = new LiveComboBox(this);
     layout->addWidget(combo_);
     connect(combo_, &QComboBox::currentIndexChanged, this, &JFJochViewerROIList::OnSelectionChanged);
+    connect(combo_, &LiveComboBox::itemsReplaced, this, &JFJochViewerROIList::OnSelectionChanged);
 
     auto *buttons = new QHBoxLayout();
     type_combo_ = new QComboBox(this);
@@ -154,22 +153,21 @@ void JFJochViewerROIList::loadImage(std::shared_ptr<const JFJochReaderImage> ima
 
 void JFJochViewerROIList::RebuildCombo(const QString &keep_selected) {
     rebuilding_ = true;
-    combo_->clear();
 
     // Running index across boxes/circles/azimuthal - matches the enumeration order used by the
     // image overlay, so each item's swatch colour equals its annotation colour on the image.
-    int color_index = 0;
+    // Called on every image of a live acquisition; the combo only changes when the list does.
+    QVector<LiveComboBox::Item> items;
     auto add_item = [&](const std::string &name, const char *type) {
         // display "name · type", with the bare name kept as item data for lookups
-        QPixmap swatch(14, 14);
-        swatch.fill(ROIAnnotationColor(color_index++));
-        combo_->addItem(QIcon(swatch),
-                        QString("%1  ·  %2").arg(QString::fromStdString(name), type),
-                        QString::fromStdString(name));
+        items.push_back({QString("%1  ·  %2").arg(QString::fromStdString(name), type),
+                         QString::fromStdString(name), QString(),
+                         ROIAnnotationColor(static_cast<int>(items.size()))});
     };
     for (const auto &b : rois_.boxes) add_item(b.GetName(), "box");
     for (const auto &c : rois_.circles) add_item(c.GetName(), "circle");
     for (const auto &a : rois_.azimuthal) add_item(a.GetName(), "azim");
+    combo_->SetItems(items);
 
     if (!keep_selected.isEmpty()) {
         const int idx = combo_->findData(keep_selected);
diff --git a/viewer/widgets/JFJochViewerROIList.h b/viewer/widgets/JFJochViewerROIList.h
index c1138b13f..ecbbc4bbb 100644
--- a/viewer/widgets/JFJochViewerROIList.h
+++ b/viewer/widgets/JFJochViewerROIList.h
@@ -13,6 +13,7 @@
 #include "JFJochViewerROIResult.h"
 #include "../../common/ROIDefinition.h"
 #include "../../reader/JFJochReaderImage.h"
+#include "LiveComboBox.h"
 
 // Manages the dataset's ROI list: select one, add (box/circle/azimuthal), rename or
 // delete, and show the selected ROI's statistics for the current image. Edits are
@@ -21,7 +22,7 @@
 class JFJochViewerROIList : public QWidget {
     Q_OBJECT
 
-    QComboBox *combo_;
+    LiveComboBox *combo_;
     QComboBox *type_combo_;
     QLabel *flabel_[4];
     QLineEdit *fedit_[4];
diff --git a/viewer/widgets/LiveComboBox.cpp b/viewer/widgets/LiveComboBox.cpp
new file mode 100644
index 000000000..9884bb539
--- /dev/null
+++ b/viewer/widgets/LiveComboBox.cpp
@@ -0,0 +1,71 @@
+// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only
+
+#include "LiveComboBox.h"
+
+#include <QAbstractItemView>
+#include <QEvent>
+#include <QIcon>
+#include <QPixmap>
+#include <QSignalBlocker>
+#include <QTimer>
+
+LiveComboBox::LiveComboBox(QWidget *parent) : QComboBox(parent) {
+    // The popup is a separate window holding the view. Not every way of closing it goes through
+    // hidePopup() (a click outside just hides the window), so watch the window itself.
+    view()->window()->installEventFilter(this);
+}
+
+bool LiveComboBox::SetItems(const QVector<Item> &items) {
+    if (view()->isVisible()) {
+        pending_ = items;
+        return false;
+    }
+    pending_.reset();
+    if (items == items_)
+        return false;
+    Replace(items);
+    return true;
+}
+
+void LiveComboBox::Replace(const QVector<Item> &items) {
+    QSignalBlocker blocker(this);
+    const QVariant selected = currentData();
+    clear();
+    for (const auto &item : items) {
+        if (item.separator) {
+            insertSeparator(count());
+            continue;
+        }
+        if (item.swatch.isValid()) {
+            QPixmap pixmap(14, 14);
+            pixmap.fill(item.swatch);
+            addItem(QIcon(pixmap), item.text, item.data);
+        } else
+            addItem(item.text, item.data);
+        if (!item.tooltip.isEmpty())
+            setItemData(count() - 1, item.tooltip, Qt::ToolTipRole);
+    }
+    items_ = items;
+    const int index = selected.isValid() ? findData(selected) : -1;
+    setCurrentIndex(index >= 0 ? index : (count() > 0 ? 0 : -1));
+}
+
+void LiveComboBox::ApplyPending() {
+    if (!pending_ || view()->isVisible())
+        return;
+    const QVector<Item> items = std::move(*pending_);
+    pending_.reset();
+    if (items == items_)
+        return;
+    Replace(items);
+    emit itemsReplaced();
+}
+
+bool LiveComboBox::eventFilter(QObject *watched, QEvent *event) {
+    // Queued: a click on an item hides the popup first and selects the item afterwards, so the
+    // held-back items go in once the pick has landed, and keep it.
+    if (event->type() == QEvent::Hide && pending_)
+        QTimer::singleShot(0, this, &LiveComboBox::ApplyPending);
+    return QComboBox::eventFilter(watched, event);
+}
diff --git a/viewer/widgets/LiveComboBox.h b/viewer/widgets/LiveComboBox.h
new file mode 100644
index 000000000..df203e300
--- /dev/null
+++ b/viewer/widgets/LiveComboBox.h
@@ -0,0 +1,43 @@
+// SPDX-FileCopyrightText: 2026 Filip Leonarski, Paul Scherrer Institute <filip.leonarski@psi.ch>
+// SPDX-License-Identifier: GPL-3.0-only
+
+#pragma once
+
+#include <QComboBox>
+#include <QColor>
+#include <QVector>
+
+#include <optional>
+
+// A combo box whose items are refreshed by live updates. SetItems() leaves the items alone when
+// they are unchanged, and while the popup is open it holds the change back until the popup has
+// closed, so a live update never closes the dropdown or moves the selection under the user.
+// Replacing the items keeps the selection by item data (the first item when it is gone) and emits
+// no currentIndexChanged; a replacement held back over an open popup emits itemsReplaced() instead.
+class LiveComboBox : public QComboBox {
+    Q_OBJECT
+public:
+    struct Item {
+        QString text;
+        QVariant data;
+        QString tooltip;
+        QColor swatch;           // shown as a small square icon when valid
+        bool separator = false;
+        bool operator==(const Item &other) const = default;
+    };
+
+    explicit LiveComboBox(QWidget *parent = nullptr);
+    // True if the items were replaced now; false if unchanged or held back for an open popup.
+    bool SetItems(const QVector<Item> &items);
+
+signals:
+    void itemsReplaced();
+
+private:
+    QVector<Item> items_;
+    std::optional<QVector<Item>> pending_;
+
+    void Replace(const QVector<Item> &items);
+    void ApplyPending();
+    bool eventFilter(QObject *watched, QEvent *event) override;
+};
diff --git a/viewer/widgets/PowderCalibrationWidget.cpp b/viewer/widgets/PowderCalibrationWidget.cpp
index d40f4aeec..3acbe83d0 100644
--- a/viewer/widgets/PowderCalibrationWidget.cpp
+++ b/viewer/widgets/PowderCalibrationWidget.cpp
@@ -13,7 +13,7 @@
 PowderCalibrationWidget::PowderCalibrationWidget(QWidget *parent) : QWidget(parent) {
     auto layout = new QVBoxLayout(this);
 
-    calibrantCombo = new QComboBox(this);
+    calibrantCombo = new LiveComboBox(this);
     // Without this a combo asks to be as wide as its longest entry - and it is never allowed to
     // shrink below that, which is what used to pin the whole settings dock wide as soon as the
     // powder section was expanded. The current text elides instead; the tooltip carries the rest.
@@ -107,24 +107,24 @@ CalibrationSelection PowderCalibrationWidget::Selection() const {
 }
 
 void PowderCalibrationWidget::updateCalibrantList() {
-    calibrantCombo->clear();
-
+    // Called for every image, live ones included: the combo only changes when the list does, and
+    // keeps the user's calibrant by name.
+    QVector<LiveComboBox::Item> items;
     for (const auto &c : Calibrants())
-        calibrantCombo->addItem(QString::fromStdString(c.name));
+        items.push_back({QString::fromStdString(c.name), QString::fromStdString(c.name)});
     if (sample_cell) {
         // The cell goes in the tooltip, not in the entry: a 40-character item would set the combo's
         // minimum width and, through it, the minimum width of the dock this widget sits in.
-        calibrantCombo->addItem("Current sample cell");
-        calibrantCombo->setItemData(calibrantCombo->count() - 1,
-            QString("%1 %2 %3 %4 %5 %6")
-                .arg(QString::number(sample_cell->a, 'f', 1))
-                .arg(QString::number(sample_cell->b, 'f', 1))
-                .arg(QString::number(sample_cell->c, 'f', 1))
-                .arg(QString::number(sample_cell->alpha, 'f', 1))
-                .arg(QString::number(sample_cell->beta, 'f', 1))
-                .arg(QString::number(sample_cell->gamma, 'f', 1)), Qt::ToolTipRole);
+        items.push_back({"Current sample cell", "Current sample cell",
+                         QString("%1 %2 %3 %4 %5 %6")
+                             .arg(QString::number(sample_cell->a, 'f', 1))
+                             .arg(QString::number(sample_cell->b, 'f', 1))
+                             .arg(QString::number(sample_cell->c, 'f', 1))
+                             .arg(QString::number(sample_cell->alpha, 'f', 1))
+                             .arg(QString::number(sample_cell->beta, 'f', 1))
+                             .arg(QString::number(sample_cell->gamma, 'f', 1))});
     }
-    calibrantCombo->setCurrentIndex(0);
+    calibrantCombo->SetItems(items);
 }
 
 void PowderCalibrationWidget::loadImage(std::shared_ptr<const JFJochReaderImage> image) {
diff --git a/viewer/widgets/PowderCalibrationWidget.h b/viewer/widgets/PowderCalibrationWidget.h
index a4be9cc23..2ec7014b4 100644
--- a/viewer/widgets/PowderCalibrationWidget.h
+++ b/viewer/widgets/PowderCalibrationWidget.h
@@ -11,6 +11,7 @@
 #include "../../common/UnitCell.h"
 #include "../../reader/JFJochReaderImage.h"
 #include "../../image_analysis/geom_refinement/PowderCalibration.h"   // CalibrationMethod
+#include "LiveComboBox.h"
 
 // What a whole-dataset calibration run is set to. The analysis library takes the calibrant as a ring
 // list rather than a name (ice has no cell to enumerate rings from), so the name is resolved here.
@@ -31,7 +32,7 @@ class PowderCalibrationWidget : public QWidget {
     // the group's absences, or the fit pairs the innermost OBSERVED ring with a forbidden one.
     std::optional<gemmi::SpaceGroup> sample_sg;
 
-    QComboBox* calibrantCombo{nullptr}; // stores current calibrant selection
+    LiveComboBox* calibrantCombo{nullptr}; // stores current calibrant selection
     QComboBox* methodCombo{nullptr};    // rings / spots, for the whole-dataset run
     QCheckBox* refineTiltCheck{nullptr};// fit the detector tilt, or hold it where it is
 
diff --git a/viewer/windows/JFJochCalibrationWindow.cpp b/viewer/windows/JFJochCalibrationWindow.cpp
index 50ded0fcb..d53fccfce 100644
--- a/viewer/windows/JFJochCalibrationWindow.cpp
+++ b/viewer/windows/JFJochCalibrationWindow.cpp
@@ -17,7 +17,7 @@ JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelper
 
     viewer = new JFJochSimpleImage(this);
 
-    calibration_option = new QComboBox(this);
+    calibration_option = new LiveComboBox(this);
     color_map_select = new QComboBox(this);
 
     color_map_select->addItem("Viridis", static_cast<int>(ColorScaleEnum::Viridis));
@@ -61,6 +61,9 @@ JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelper
     });
 
     connect(calibration_option, &QComboBox::currentIndexChanged, this, &JFJochCalibrationWindow::CalibrationSelected);
+    connect(calibration_option, &LiveComboBox::itemsReplaced, this, [this] {
+        CalibrationSelected(calibration_option->currentIndex());
+    });
     centralWidget->setLayout(grid_layout);
 
     statusBar = new QStatusBar(this);
@@ -73,13 +76,15 @@ JFJochCalibrationWindow::JFJochCalibrationWindow(QWidget *parent) : JFJochHelper
 void JFJochCalibrationWindow::datasetLoaded(std::shared_ptr<const JFJochReaderDataset> in_dataset) {
     dataset = std::move(in_dataset);
 
-    QSignalBlocker b(calibration_option);
-    calibration_option->clear();
+    // Arrives on every dataset tick of a live acquisition; the combo only changes when the list
+    // does, and keeps the selection by name.
+    QVector<LiveComboBox::Item> items;
     if (dataset) {
-        calibration_option->addItem("Pixel mask");
+        items.push_back({"Pixel mask", "Pixel mask"});
         for (auto &calibration : dataset->calibration_data)
-            calibration_option->addItem(calibration.c_str());
+            items.push_back({calibration.c_str(), calibration.c_str()});
     }
+    calibration_option->SetItems(items);
 
     // Rebuilding the mask is a full-detector copy plus a full-resolution recolour on the GUI
     // thread, and this arrives on every dataset tick when following a live acquisition. Do not pay
@@ -88,14 +93,14 @@ void JFJochCalibrationWindow::datasetLoaded(std::shared_ptr<const JFJochReaderDa
         pending_mask_reload = true;
         return;
     }
-    LoadMask();
+    CalibrationSelected(calibration_option->currentIndex());   // the user's pick, not always the mask
 }
 
 void JFJochCalibrationWindow::showEvent(QShowEvent *event) {
     JFJochHelperWindow::showEvent(event);
     if (pending_mask_reload) {
         pending_mask_reload = false;
-        LoadMask();
+        CalibrationSelected(calibration_option->currentIndex());
     }
 }
 
@@ -116,7 +121,7 @@ void JFJochCalibrationWindow::LoadMask() {
 }
 
 void JFJochCalibrationWindow::CalibrationSelected(int val) {
-    if (val == 0)
+    if (val <= 0)
         LoadMask();
     else
         emit loadCalibration(calibration_option->itemText(val));
diff --git a/viewer/windows/JFJochCalibrationWindow.h b/viewer/windows/JFJochCalibrationWindow.h
index 577f86b74..334a598ac 100644
--- a/viewer/windows/JFJochCalibrationWindow.h
+++ b/viewer/windows/JFJochCalibrationWindow.h
@@ -5,6 +5,7 @@
 
 #include <QMainWindow>
 #include <QComboBox>
+#include "../widgets/LiveComboBox.h"
 #include <QString>
 #include <QStatusBar>
 
@@ -17,7 +18,7 @@
 class JFJochCalibrationWindow : public JFJochHelperWindow {
     Q_OBJECT
 
-    QComboBox *calibration_option;
+    LiveComboBox *calibration_option;
     QComboBox *color_map_select;
     SliderPlusBox *foreground_slider;
     SliderPlusBox *background_slider;