diff -r f4b03295b1d9 -r c20c2c4c0c63 mercurial/dispatch.py
--- a/mercurial/dispatch.py	Wed Jul 14 19:44:49 2010 +0200
+++ b/mercurial/dispatch.py	Wed Jul 14 20:41:01 2010 +0200
@@ -398,6 +398,8 @@
     # 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)