Endermen teleporting when set on fire by a Fire Aspect sword.

With my Fire Aspect sword, I went outside to kill mobs (namely Endermen). Upon encountering Endermen, I would hit them (in the legs)with my Fire Aspect sword only to have them teleport away on fire, never to be seen again. I encountered many Endermen that night, 10 or so. All of them teleported upon getting set on fire from my sword.