It's a problem at twink brackets with rated arenas, as well (70, 80, 85). If a player on a team does not have their experience turned on, they will not be able to accept the queue.
With rated arenas in those twinking brackets, they will receive deserter when attempting to accept the queue.
I hypothesize that the problem is that F2Ps are both XP off/on simultaneously, which is why we cannot do wargame battlegrounds in the first place. This phenomenon is now causing us problems due to whatever bug was created when Blizzard edited the code surrounding deserter debuffs.
I think the problem will be fixed soon.