User/Guest Problem,

Hi, ive got a slight user problem. Today I had someone called 'Ghost' post on the forums asking a question; hes done nothing wrong as far as I know accept he is not a registered user, does not appear in the userlist or within the Database, yet it says hes a 'Member', the only reason I noticed it was that when he edited a post instead of leaving his name it was edited by a 'Guest'.

Ive checked the forum permissions, and its setup in theory that you have to be a registered user to post, accept when I logged out to try myself I could also leave a new message as a forum Guest (accept it would say im a member). Any ideas what might be causing this?

Cheers!