diff --git a/rugnux/RugnuxPasses.cpp b/rugnux/RugnuxPasses.cpp
index a1f73d2ec..212851a93 100644
--- a/rugnux/RugnuxPasses.cpp
+++ b/rugnux/RugnuxPasses.cpp
@@ -912,21 +912,22 @@ std::optional<ProcessResult> Rugnux::RefinedPasses(RugnuxObserver *observer, Pro
             // The demoted arm runs first, as a probe: it is compared on the post-refinement's held-out
             // residual, so it has to measure one, and a canonical pass only does where the pre-pass
             // moved the geometry. The canonical pass below is the promoted arm (lattice_arm_check_).
-            const bool probe_was = postrefine_probe_;
-            postrefine_probe_ = true;
-            postrefine_probe_only_ = true;
+            // The probe runs on a copy of the run, so it leaves nothing on the run - not the spot
+            // budget its first pass measures, which the canonical pass would otherwise start from -
+            // except the geometry its post-refinement asks for, which the promoted arm reads (see
+            // ScaleMergeAndSymmetry), and its first-pass memo.
+            Rugnux demoted_run(*this);
+            demoted_run.postrefine_probe_ = true;
+            demoted_run.postrefine_probe_only_ = true;
             IndexingSettings demoted_settings = experiment_.GetIndexingSettings();
             demoted_settings.LatticeClassDemoted(length_arm);
-            experiment_.ImportIndexingSettings(demoted_settings);
-            lattice_angles_demoted_ = angle_arm;
-            demoted_arm = RunPipeline(observer, /*write_output=*/false, /*geometry_prepass=*/false);
+            demoted_run.experiment_.ImportIndexingSettings(demoted_settings);
+            demoted_run.lattice_angles_demoted_ = angle_arm;
+            demoted_arm = demoted_run.RunPipeline(observer, /*write_output=*/false, /*geometry_prepass=*/false);
             ++arm_passes;
-            postrefine_probe_only_ = false;
-            postrefine_probe_ = probe_was;
-            IndexingSettings promoted_settings = experiment_.GetIndexingSettings();
-            promoted_settings.LatticeClassDemoted(false);
-            experiment_.ImportIndexingSettings(promoted_settings);
-            lattice_angles_demoted_ = false;
+            prepass_detector_geometry_ = demoted_run.prepass_detector_geometry_;
+            for (const auto &m : demoted_run.first_pass_memo_)
+                AddFirstPassMemo(m);
             lattice_arm_check_ = LatticeArmCheck{.demoted = demoted_arm->post_refine};
         } else {
             logger.Info("Metric symmetry: {} - the free refinement departs from it by {:.2f} {}, "
@@ -942,6 +943,7 @@ std::optional<ProcessResult> Rugnux::RefinedPasses(RugnuxObserver *observer, Pro
                 base_prefix);
     speculate_geometry_probe_ = true;   // a walk that follows starts with an indexing probe
     rerun_if_starved_ = true;
+    const DiffractionExperiment before_pass2 = experiment_;
     auto pass2 = RunPipeline(observer, /*write_output=*/true, /*geometry_prepass=*/false);
     if (lattice_arm_check_) {
         // The metric-symmetry check above, decided inside the pass just run (the promoted arm).
@@ -970,8 +972,10 @@ std::optional<ProcessResult> Rugnux::RefinedPasses(RugnuxObserver *observer, Pro
                     length_arm ? "axes" : "an angle", length_arm ? 100.0 * split : split * 180.0 / PI,
                     length_arm ? "% apart" : "deg from 90",
                     demoted_class, realised_demoted, realised_promoted);
-            // The promoted arm stopped before its merge; the demoted class is the canonical pass.
+            // The promoted arm stopped before its merge; the demoted class is the canonical pass, and
+            // it starts where the promoted one did, not from the spot budget that one measured.
             ++arm_passes;
+            experiment_ = before_pass2;
             IndexingSettings demoted_settings = experiment_.GetIndexingSettings();
             demoted_settings.LatticeClassDemoted(length_arm);
             experiment_.ImportIndexingSettings(demoted_settings);