As an experiment, I created a user named 'kepstin/bot' to use as a bot account.

When I attempt to view its user page, at http://musicbrainz.org/user/kepstin%2Fbot it instead shows me the user page for 'kepstin' - and none of the other subpages, such as edit list or collections are accessible.

(One reasonable 'fix' for this issue would be to disallow / in usernames, imo.)