Patch anchoring does not work for "hg diff"

The patch appears to be anchored correctly, but crucible doesn't acutally link to the correct revision:

Note the date of the first revision is shown, rather than the revision id.

The patch header looks something like:

diff -r 1605d49703e5 ReleaseProcedure.txt
--- a/ReleaseProcedure.txt      Sun Aug 08 15:17:49 2010 -0500
+++ b/ReleaseProcedure.txt      Wed Oct 13 11:14:34 2010 +1100

The first line contains the revision id we should be anchoring against.