Mark, splitting a topic gets to be a pain because it depends on who each one replied to. If everyone replies to the original post, it's easy. If everyone replies to the last post, it's easy. But if anyone uses quickquote or quickreply from an individual post anywhere in the thread it can create a thread with multiple branches.
That's where it tends to end up messy, since you'll move one post and might end up with half the thread coming along with it. Move one of those out and you might end up with the same thing.
When it comes to moving, if you really want to see what ones are coming with it, a good way for now is to pop over to threaded mode and you can see all the replies that are on that particular branch you're going to be splitting off.
