I recently switched to requiring user registration to comment ... many of my readers registered, one could not. When I attempted to create a new user for him, the 'repeat password' box indicated a mismatch instantly.
I know this is a recurring bug, because it has come up before in other forums.
My reader cannot register, either, doesn't get an email with a new password.
BTW: I could not log on wi/ my usual username on this forum b/c the password issued by the Wordpress server was not recognized over here (I had to re-register).