not sure why it would do this - i dont think its related to be honest. As far as i can see this is an unhacked forum - if there is a problem, running the upgrade file could help
ive been running vbulletin sites for about 4 years now - ive got about 4 owned licenses presently. If your having problems with this sort of thing please pm me as theres a good chance that ive had the same problem in the past (my 2nd vbulletin site was over 5000 members and i had applied about 50 hacks to it!) and if not ill be able to point you in the right direction