This thread should help.
http://www.beehiveforum.us/forums/messages.php?webtag=INFO&msg=13.1
The box to the right of Forum Style in the Style section of Forum Options in My Controls must have been checked. I've done it myself, and had to go through and reset all the forums I didn't want to use a particular style.
I'm going to see if I can find the code that handles that part and see if I can uncheck those boxes. They're check by default, but I think it would be better if they weren't.