I actually found a bug today, well, one of my forum users did:
1) Set up more than one prefix for a sub-forum
2) start a thread with any content
3) Select one prefix (any one except the first)
4) Post the thread
5) Edit the post
6) go to "more options"
7) make any change and save it
the prefix will revert to the 1st on in the list (#1 in styling priority)
Do the same steps again and then in #7 change the prefix to "no prefix" to clear the prefixes, then change it back to the one you wanted (same selected in #3). Save it, it will revert to the #1 again.
No matter what you do, you can't save the prefix you want via the More Options / advanced editor. In the overlay, it works, no problem. Most people use the overlay so this is not a huge bug, but a bug nonetheless...