The Admin tool for attaching one forum post to another one should be moved from a generic section at the top, and instead be placed on post specifically. http://www.angelfire.com/hero/straygames/ByondBugs/ AttachingForumPosts.png
The current placement is not only misleading, but its quite annoying to have to go through the topic, get the ID of the post you want to reattach, carefully paste it into the address bar, reload the page, and then go back to the other topic to get the ID of the post you want to attach it to.
It would also be nice if you could attach posts to ones in other forum categories. I'm not really sure why this isn't already do-able. If it isn't possible to do in a straightforward manner because of the way your forums are setup, then it should at least be possible for the system to automatically attach the post to 0 (making it a new thread when necessary), move that new thread to the other category, and then attach it to the desired post?
There's also some odd bug where when I paste the ID for the new thread into the New Parent ID: input box, that entire section will just disappear. But I haven't really figured out how/why this happens, or how to consistently reproduce the issue for testing.