No, we're pretty sure it's the AI for the baddies. I'm guessing that by zooming in that the amount of baddies being processed gets reduced, but it also doesn't make sense that it doesn't do it on all levels. Might be some bad garbage collection.
Nah, I only went down 2 or 3 floors. I found this just before I went to bed and gave it a quick spin. I like that you can go back up floors after you go down, though.