--- a/hgext3rd/topic/__init__.py	Fri Nov 20 21:38:48 2020 +0100
+++ b/hgext3rd/topic/__init__.py	Tue Dec 22 20:22:41 2020 -0500
@@ -435,6 +435,13 @@
         repo.ui.setconfig(b'experimental', b'thg.displaynames', b'topics',
                           source=b'topic-extension')
 
+    # BUG: inmemory rebase drops the topic, and fails to switch to the new
+    # topic.  Disable inmemory rebase for now.
+    if repo.ui.configbool(b'rebase', b'experimental.inmemory'):
+        repo.ui.setconfig(b'rebase', b'experimental.inmemory', b'False',
+                          source=b'topic-extension')
+
+
     class topicrepo(repo.__class__):
 
         # attribute for other code to distinct between repo with topic and repo without