1 files changed, 20 insertions, 5 deletions

diff --git a/source/blender/blenkernel/intern/nla.c b/source/blender/blenkernel/intern/nla.c
index 8f54d71108a..10abb8f20df 100644
--- a/source/blender/blenkernel/intern/nla.c
+++ b/source/blender/blenkernel/intern/nla.c
@@ -252,12 +252,15 @@ static NlaStrip *find_active_strip_from_listbase(const NlaStrip *active_strip,
                                                  const ListBase /* NlaStrip */ *strips_source,
                                                  const ListBase /* NlaStrip */ *strips_dest)
 {
+  BLI_assert_msg(BLI_listbase_count(strips_source) == BLI_listbase_count(strips_dest),
+                 "Expecting the same number of source and destination strips");
+
   NlaStrip *strip_dest = strips_dest->first;
   LISTBASE_FOREACH (const NlaStrip *, strip_source, strips_source) {
     if (strip_dest == NULL) {
-      /* The tracks are assumed to have an equal number of strips, but this is not the case when
-       * dragging multiple strips. The transform system merges the selected strips into one
-       * meta-strip, reducing the number of strips in `track_dest`. */
+      /* The tracks are assumed to have an equal number of strips, but this is
+       * not the case. Not sure when this might happen, but it's better to not
+       * crash. */
       break;
     }
     if (strip_source == active_strip) {
@@ -282,7 +285,9 @@ static NlaStrip *find_active_strip_from_listbase(const NlaStrip *active_strip,
   return NULL;
 }
 
-/* Set adt_dest->actstrip to the strip with the same index as adt_source->actstrip. */
+/* Set adt_dest->actstrip to the strip with the same index as
+ * adt_source->actstrip. Note that this always sets `adt_dest->actstrip`; sets
+ * to NULL when `adt_source->actstrip` cannot be found. */
 static void update_active_strip(AnimData *adt_dest,
                                 NlaTrack *track_dest,
                                 const AnimData *adt_source,
@@ -298,6 +303,12 @@ static void update_active_strip(AnimData *adt_dest,
 /* Set adt_dest->act_track to the track with the same index as adt_source->act_track. */
 static void update_active_track(AnimData *adt_dest, const AnimData *adt_source)
 {
+  adt_dest->act_track = NULL;
+  adt_dest->actstrip = NULL;
+  if (adt_source->act_track == NULL && adt_source->actstrip == NULL) {
+    return;
+  }
+
   BLI_assert(BLI_listbase_count(&adt_source->nla_tracks) ==
              BLI_listbase_count(&adt_dest->nla_tracks));
 
@@ -306,7 +317,11 @@ static void update_active_track(AnimData *adt_dest, const AnimData *adt_source)
     if (track_source == adt_source->act_track) {
       adt_dest->act_track = track_dest;
     }
-    update_active_strip(adt_dest, track_dest, adt_source, track_source);
+
+    /* Only search for the active strip if it hasn't been found yet. */
+    if (adt_dest->actstrip == NULL && adt_source->actstrip != NULL) {
+      update_active_strip(adt_dest, track_dest, adt_source, track_source);
+    }
 
     track_dest = track_dest->next;
   }