Split posts assigns new ID to original thread.
I just split a post from a thread and noticed that the ID of the original post changed and the new thread has the ID of the original thread.
It should be the other way around. If someone links to a thread via URL they should go to the original thread. We don't want people to jump to a post that is split from that original thread, if it's split from the thread it's probably a completely different/unrelated topic.

