http authorization always fails

This may be the same issue as <<issue 683>> - it's hard to tell - but I've been unable to push to Bitbucket.org using HTTPS for at least a month (the same password works for the normal web UI). Using SSH works as expected so this hasn't been a major issue for me but it doesn't appear to be <<issue 939>> as there isn't a proxy involved.

Mercurial Distributed SCM (version 1.5.1)
Mac OS X 10.6.3