Oops. Yeah, "Region Zero" is probably the head of some sort of stack/heap/list which isn't supposed to be accessable by the player. It may be "protected" from selection via the same methods used to "protect" the Ronin provinces. So when you nullify one protection, you do the same to the other. Oops. (Just a guess, here, remember.)

Another thing to keep your eye out for: When there's an uprising, then (at least in vanilla STW) you cannot select that army the very next turn. Well, if you're playing Ronin you can BUT.... crash to desktop in almost every case. :(