Take a look at the 11th reply to the topic on the first page - that is an actual impossibility in UBB-land, so something is VERY wrong here...
Please open up a support ticket - the link is in my signature. I'll need FTP access in order to diagnose and solve this one.
Forum & topic numbers of similarly corrupted topics would also be handy, as well as knowing whether posts were eaten before and are simply now being reflected... rather, if there is actual post munching going on in topics created after the upgrade. Existing pre-corrupted topics would probably only yeild problems.
UBB.classic™ DeveloperHaving problems? Open up a support ticket!