Umm, wasn't that the original question of this thread already?
The problem is that it poses too many possible problems for very little payback(IMO). The real question in my mind is WHY? Why would someone want to have their two characters fight one another? Since the rules have banned this kind of interaction already anyway to prevent these possible abuses, the only reason I can think of is IC reasons. And if that is the only reason, then an unofficial fight serves just as well as an official fight while avoiding any possibility of abuse.
Well mostly just as part of an IC reason could conflict strictly with an unoffical fight result, such as yen or whatnot (which is specifically the situation and why DraDra keeps fighting Gray ).