From my understanding a thread update does not delete any posts. So if you deleted a user his posts would still remain, unless you ran a 'delete all posts by user' before you deleted the user.
I was lucky to have in production a minuscule BBS. So I was able to identify the users I deleted and quickly identify the posts by them in the prune posts view. On a board that has a lot of users and posts this is a nightmare, I most certainly agree. But I am 99% sure this is the cause.
Why this was not caught in the private beta trails though escapes me. I am sure Infopop is inundated with trouble tickets. But this one should be at the very top of the list, with high priority.
