What is the rule for a thread self moderate to suddenly become a normal one ?
This (I don't think your case falls under this, am I right?):
The selfMod bit will now be permanently cleared when a non-mod moves a topic into a section which doesn't allow selfMod.
Can a local moderator do it? (I try to find a solution, it's so weird..)
I don't know but you should move this thread to "Meta".