I lost several posts also. Normally it says guest removed post, but mine were just gone. Mabey the entire threads are being deleted at once. I changed my password. I did read that bad bear was cleaning/deleting some stuff. I think Theymos gives him executive power to clean some alts up, he's not meaning anything bad.
If a thread is deleted (threads are deleted because an account gets "nuked" that created the account) then all the posts that replied to the thread will be deleted as well, although you will not be notified.
*Another reason that a thread could be deleted is that it somehow is breaking forum rules - such as was created for begging, is discussing how to access an illegal site, ect