diff --git a/src/aare/gui/main_window.py b/src/aare/gui/main_window.py
index 41ed7607..4022bbed 100644
--- a/src/aare/gui/main_window.py
+++ b/src/aare/gui/main_window.py
@@ -385,7 +385,8 @@ class MainWindow(QMainWindow):
                 banner = TitleLabel(title, holder)
                 banner.setCursor(Qt.CursorShape.PointingHandCursor)
                 banner.setToolTip("Only accessible for beamline scientists")
-                banner.installEventFilter(self)
+                # eventFilter install happens LATE in __init__ (next to
+                # installEventFilter(self)) — see the comment there.
                 holder_layout.addWidget(banner)
                 beamline_layout.addWidget(holder)
                 self._locked_beamline_banners.append(banner)
@@ -403,10 +404,6 @@ class MainWindow(QMainWindow):
 
         self.left_column_tabs.addTab(beamline_page, "Beamline")
         self.left_column_tabs.addTab(experiment_page, "Experiment")
-        # A click on the pgroup-gated (disabled) Beamline tab is otherwise
-        # eaten silently by the tab bar — the filter pops the explanation
-        # instead (same pattern as the Auxiliary-puck tab).
-        self.left_column_tabs.tabBar().installEventFilter(self)
 
         # Only the visible page counts toward the height — same trick as the
         # content stack below, else the taller page pads the other tab.
@@ -431,6 +428,7 @@ class MainWindow(QMainWindow):
             # first widget now, not samcam.
             else self._locked_beamline_banners[0].parentWidget()
         )
+        assert beamline_first is not None  # the locked banner always has its holder
         for first in (beamline_first, self.data_collection, self.data_collection.file_path_panel):
             first_layout = first.layout()
             assert first_layout is not None  # panels build their layouts in __init__
@@ -887,6 +885,15 @@ class MainWindow(QMainWindow):
         self.daq = DAQWorker(base_url=self._base_url, token=self._token)
 
         self.installEventFilter(self)
+        # These share MainWindow.eventFilter, which reads sample_lists_tabs
+        # and left_column_tabs on every event — so they must install only
+        # HERE, after every attribute the filter touches exists. Installing
+        # them at widget-construction time made each early event raise
+        # AttributeError inside the filter ("Error calling Python override
+        # of QObject::eventFilter()" spam that poisoned CI teardowns).
+        self.left_column_tabs.tabBar().installEventFilter(self)
+        for locked_banner in self._locked_beamline_banners:
+            locked_banner.installEventFilter(self)
 
         self._idle_timer = QTimer(self)
         self._idle_timer.setInterval(60_000)
@@ -3217,35 +3224,42 @@ class MainWindow(QMainWindow):
                 self._mark_user_interaction()
         except Exception as e:
             logger.debug(f"GUI interaction event filter error: {e}", exc_info=True)
-        # Non-staff click on the greyed-out Auxiliary-puck tab: only installed
-        # for non-staff, and tabAt() is geometric so it still sees the
-        # disabled tab — explain the lock instead of silently eating the click.
-        sample_tab_bar = self.sample_lists_tabs.tabBar()
-        if (
-            event.type() == QEvent.Type.MouseButtonPress
-            and sample_tab_bar is not None
-            and obj is sample_tab_bar
-            and sample_tab_bar.tabAt(event.position().toPoint()) == 1
-        ):
-            self._show_reference_tools_staff_only_popup()
-            return True
-        # Non-staff click on a locked Beamline banner: same treatment as the
-        # Auxiliary-puck tab — explain the gate instead of eating the click.
-        if event.type() == QEvent.Type.MouseButtonPress and obj in self._locked_beamline_banners:
-            self._show_beamline_staff_only_popup()
-            return True
-        # Click on the pgroup-gated (disabled) Beamline tab: tabAt() is
-        # geometric, so it still sees the disabled tab under the cursor.
-        left_tab_bar = self.left_column_tabs.tabBar()
-        if (
-            event.type() == QEvent.Type.MouseButtonPress
-            and left_tab_bar is not None
-            and obj is left_tab_bar
-            and left_tab_bar.tabAt(event.position().toPoint()) == 0
-            and not self.left_column_tabs.isTabEnabled(0)
-        ):
-            self._show_beamline_tab_gated_popup()
-            return True
+        # getattr defaults: this filter also runs for events delivered while
+        # __init__ is still building (or teardown is tearing down) the very
+        # widgets it inspects — a raise here spams every event and breaks
+        # widget cleanup, so missing attributes must mean "not my click".
+        if event.type() == QEvent.Type.MouseButtonPress:
+            # Non-staff click on the greyed-out Auxiliary-puck tab: only
+            # installed for non-staff, and tabAt() is geometric so it still
+            # sees the disabled tab — explain the lock instead of silently
+            # eating the click.
+            sample_tabs = getattr(self, "sample_lists_tabs", None)
+            sample_tab_bar = sample_tabs.tabBar() if sample_tabs is not None else None
+            if (
+                sample_tab_bar is not None
+                and obj is sample_tab_bar
+                and sample_tab_bar.tabAt(event.position().toPoint()) == 1
+            ):
+                self._show_reference_tools_staff_only_popup()
+                return True
+            # Non-staff click on a locked Beamline banner: same treatment as
+            # the Auxiliary-puck tab — explain the gate, don't eat the click.
+            if obj in getattr(self, "_locked_beamline_banners", ()):
+                self._show_beamline_staff_only_popup()
+                return True
+            # Click on the pgroup-gated (disabled) Beamline tab: tabAt() is
+            # geometric, so it still sees the disabled tab under the cursor.
+            left_tabs = getattr(self, "left_column_tabs", None)
+            if left_tabs is not None:
+                left_tab_bar = left_tabs.tabBar()
+                if (
+                    left_tab_bar is not None
+                    and obj is left_tab_bar
+                    and left_tab_bar.tabAt(event.position().toPoint()) == 0
+                    and not left_tabs.isTabEnabled(0)
+                ):
+                    self._show_beamline_tab_gated_popup()
+                    return True
         return super().eventFilter(obj, event)
 
     def _start_remote_close_countdown(
diff --git a/tests/unit/gui/test_main_window.py b/tests/unit/gui/test_main_window.py
index 10516ad9..c1cd7040 100644
--- a/tests/unit/gui/test_main_window.py
+++ b/tests/unit/gui/test_main_window.py
@@ -50,6 +50,27 @@ def test_main_window_init(qtbot, mock_ui_state):
         assert win.windowTitle() == "AareGUI"
         assert win.isVisible()
 
+        # Staff-side gate behaviors piggyback on this window: every extra
+        # MainWindow construction raises the odds of the PySide SystemError
+        # flake, so don't build another one just for these.
+        from aarecommon.models.models import BeamlineStateEnum
+
+        with patch("aare.gui.main_window.QMessageBox") as popup:
+            win._show_beamline_tab_gated_popup()
+            assert popup.information.called, "staff popup must explain the visitor pgroup"
+
+        win._apply_default_sample_tab(BeamlineStateEnum.BeamLocation)
+        assert win.sample_lists_tabs.currentIndex() == 1  # Auxiliary puck
+        win._apply_default_sample_tab(BeamlineStateEnum.DataCollection)
+        assert win.sample_lists_tabs.currentIndex() == 0
+
+        # Energy row inside Exp. Config. emits eV (the GUI shows keV)
+        sent = []
+        win.data_collection.change_energy.connect(sent.append)
+        win.data_collection.energy_spin.setValue(12.4)
+        win.data_collection._emit_change_energy()
+        assert sent and abs(sent[0] - 12400.0) < 1e-6
+
 
 def test_main_window_mount_view(qtbot, mock_ui_state):
     with (
@@ -551,41 +572,8 @@ def test_nonstaff_beamline_gate_popups(qtbot, mock_ui_state):
             qtbot.mousePress(bar, Qt.MouseButton.LeftButton, pos=bar.tabRect(0).center())
             assert popup.information.called, "gated tab click must explain the gate"
 
-
-def test_staff_gated_tab_and_aux_default_tab(qtbot, mock_ui_state):
-    """Staff variants of the gates: the gated-tab popup explains the visitor
-    pgroup (not the staff gate), and alignment states raise the Auxiliary
-    puck as the default sample tab."""
-    from aarecommon.models.models import BeamlineStateEnum
-
-    with (
-        patch("requests.get"),
-        patch("aare.gui.main_window.DAQWorker"),
-        patch("aare.gui.main_window.PredictionSubscriber"),
-        patch("aare.gui.main_window.VideoThread"),
-        patch("aare.gui.main_window.JFJochDBusClient"),
-        patch("aare.gui.main_window.jwt.decode") as mock_jwt,
-    ):
-        mock_jwt.return_value = {
-            "sub": "testuser",
-            "staff": True,
-            "pgroups": ["p123"],
-            "session": 15,
-        }
-        win = _make_window(qtbot)
-
+        # The greyed-out Auxiliary-puck tab explains itself the same way.
+        aux_bar = win.sample_lists_tabs.tabBar()
         with patch("aare.gui.main_window.QMessageBox") as popup:
-            win._show_beamline_tab_gated_popup()
-            assert popup.information.called
-
-        win._apply_default_sample_tab(BeamlineStateEnum.BeamLocation)
-        assert win.sample_lists_tabs.currentIndex() == 1  # Auxiliary puck
-        win._apply_default_sample_tab(BeamlineStateEnum.DataCollection)
-        assert win.sample_lists_tabs.currentIndex() == 0
-
-        # Energy row inside Exp. Config. emits eV (the GUI shows keV)
-        sent = []
-        win.data_collection.change_energy.connect(sent.append)
-        win.data_collection.energy_spin.setValue(12.4)
-        win.data_collection._emit_change_energy()
-        assert sent and abs(sent[0] - 12400.0) < 1e-6
+            qtbot.mousePress(aux_bar, Qt.MouseButton.LeftButton, pos=aux_bar.tabRect(1).center())
+            assert popup.information.called, "aux-puck tab click must explain the lock"