hg status, hg diff do not consider an enabled keyword extension --> leads to empty commits

[rupert.thurner]

we are using mercurial as client to cvs or svn. for some files we use
keywords why we switched on the keyword extension. we update parts of
the keywords also with other means. unfortunately, hg status, hg diff
do not respect this and show "modified" or a diff:

hg init ts
cd ts
echo "\$Id\$" > kw.java
hg add
hg commit -m "kw demo"
hg kwexpand
echo "\$Id\$" > kw.java
hg diff
diff -r c3b9388a091a kw.java
--- a/kw.java   Thu Jun 04 22:05:23 2009 +0200
+++ b/kw.java   Thu Jun 04 22:10:16 2009 +0200
@@ -1,1 +1,1 @@
-$Id: kw.java,v c3b9388a091a 2009/06/04 20:05:23 oha at notpossible.com $
+$Id$

this then leads to mercurial not allowing expanding / shrinking the
keywords before committing. a commit then is empty as there the
keyword extension seems to work.

is this a bug, or do we misuse the extension?

rupert.