But my question is: Why after I uninstall a BAIN pack, there are leftovers?
I can only guess, but... have you by any chance altered any of the files that are "left over"? It could be that, if that's so, because they don't match perfectly, BAIN won't delete them by default... but I could be wrong there. Just the first thing that occurred to me. Like, say, if you'd "cleaned" them, or the like.
edit: What I was also trying to say, I suppose, is that I've never found that BAIN will do that, by default. And I've been using it for a while now...