Changing usernames

Hm - can anybody tell me what's the intended route to change a member's username? I've tried it from both ends, from phpBB's ACP and from Drupal editing the name in the user profile, but neither changed both databases. Not sure, is this how it's supposed to be, or did I break something? ;) I also noticed that sometimes Drupal won't let me edit a user profile, instead I get a message that the email address has already been taken. A prominent situation this happens to me when I try do edit Drupal's master user profile. Is this something that anyone can reproduce? Again, it may be entirely possible that this works in the original code and I botched it up myself, so sorry if that's the case. Thanks in advance!