that is not true. I know a forum who does this and has a cbox at the top that is actually tied to a post for chat and it counts toward the post count of the user and the forum. And, it was never tied to a decline of posting at said forum. As for rule breaking it would simply follow the same guidelines as the forum. while it may be deleted if it's tied to an actual thread and the cbox is just an option, it would be in the database for a staff member to see what was deleted and whatnot. Not too many chances for stuff to slip by.
