It might be a clever way to test for live forums; people are getting wiser about replying to threads started by spammers (he said, replying in a thread started by a spammer), so maybe the bots are now trying to bait moderators into banning them, and if they do, they know that the forum has active readership. That'll mean it's just a matter of finding a bot subtle enough to remain unbanned for a while.
Alternatively, it could just be someone playing silly games.
