after moving all posts from one user to a seperate subforum and then deleting that user, the viewforum.php shows for all threads where that user originally posted in wrong usernames in the last post field. it seems that the last post field is filled with the username of the first poster instead of the last poster.

some examples:
http://www.rootforum.org/forum/viewforum.php?f=100
http://www.rootforum.org/forum/viewtopic.php?f=100&t=51776
http://www.rootforum.org/forum/viewtopic.php?f=100&t=51754
http://www.rootforum.org/forum/viewtopic.php?f=100&t=51675
http://www.rootforum.org/forum/viewtopic.php?f=100&t=51555