[fel64]

He should stay logged in for a week if he’s logged in at all. Tempted to put it down to a problem on his end but that’s hasty.

Logging into bb should log you into wp and vice-versa automatically, all by itself. If not, you have a cookie problem; tell us the folder structure of your install and it can be fixed.

If you see his user in wp after he registers in bb, he must be able to log in with the same password. It reads the same entry in the database. You should never have to change their password in wp; any change to his password should be identical in bb anyway. He did register only once, right? Just once, not for both wp and bb?