diff --git a/doc/sphinxext/mne_doc_utils.py b/doc/sphinxext/mne_doc_utils.py
index b9b1e430471..7d6c545837e 100644
--- a/doc/sphinxext/mne_doc_utils.py
+++ b/doc/sphinxext/mne_doc_utils.py
@@ -13,10 +13,13 @@
 import numpy as np
 import pyvista
 import sphinx.util.logging
+from sphinx.errors import ExtensionError
 
 import mne
 from mne.utils import (
-    _assert_no_instances,
+    _assert_no_instances as _assert_no_instances_mne,
+)
+from mne.utils import (
     _get_extra_data_path,
     sizeof_fmt,
 )
@@ -104,6 +107,14 @@ def reset_warnings(gallery_conf, fname):
 t0 = time.time()
 
 
+def _assert_no_instances(cls, when):
+    """Wrap our internal one but make the traceback nicer when it fails."""
+    try:
+        _assert_no_instances_mne(cls, when)
+    except Exception as exc:
+        raise ExtensionError(str(exc)) from None
+
+
 def reset_modules(gallery_conf, fname, when):
     """Do the reset."""
     import matplotlib.pyplot as plt
diff --git a/mne/gui/_coreg.py b/mne/gui/_coreg.py
index 31bf37e496a..7480a50231d 100644
--- a/mne/gui/_coreg.py
+++ b/mne/gui/_coreg.py
@@ -10,6 +10,7 @@
 import re
 import threading
 import time
+import weakref
 from contextlib import contextmanager
 from functools import partial
 from pathlib import Path
@@ -914,7 +915,7 @@ def _on_pick(self, vtk_picker, event):
         mesh = vtk_picker.GetDataSet()
         if mesh is None or cell_id == -1 or not self._mouse_no_mvt:
             return
-        if not any(mesh is target for target in self._picking_targets):
+        if not any(mesh is target() for target in self._picking_targets):
             return
         pos = np.array(vtk_picker.GetPickPosition())
         vtk_cell = mesh.GetCell(cell_id)
@@ -1342,7 +1343,7 @@ def _add_head_surface(self):
             key = "low"
         self._update_actor("head", head_actor)
         # mark head surface mesh to restrict picking
-        self._picking_targets.append(head_surf)
+        self._picking_targets.append(weakref.ref(head_surf))
         # We need to use _get_processed_mri_points to incorporate grow_hair
         rr = self.coreg._get_processed_mri_points(key) * self.coreg._scale.T
         head_surf.points = rr