diff -r 164eb14a4a7c -r d8d0fc3988ca mercurial/dispatch.py
--- a/mercurial/dispatch.py	Wed Jul 14 19:43:31 2010 +0200
+++ b/mercurial/dispatch.py	Thu Jul 01 19:23:26 2010 -0500
@@ -388,6 +388,8 @@
     # times so we keep track of configured extensions in _loaded.
     extensions.loadall(lui)
     exts = [ext for ext in extensions.extensions() if ext[0] not in _loaded]
+    # Propagate any changes to lui.__class__ by extensions
+    ui.__class__ = lui.__class__
 
     # (uisetup and extsetup are handled in extensions.loadall)