My brother just "accedently" traded my Unzefet for one of his party pokemon. Now he cant seem to give me back my pokemon because she knows FLY. But she already knew fly, so how did this work in the first place? Am I overlooking somthing here?
Well, I wouldn't worry much if I were you. Trading a pokemon with a HM move won't affect its trading, so you may want to check its name. They're's a possibility that it had a "bad" nickname. Click here to get a list of some "bad" nicknames: http://pokemondb.net/pokebase/51546/why-cant-a-conkeldurr-be-traded-without-a-nickname' Another thing is that it may be holding an item that may prevent you trading it.
I hope this helped, but I'm a little unsure what it may actually be.