[Havn't kept up much so this might be a known bug.]
I just found out that the additional AOE dmg of the third staff auto attack skill on warrior occurs around the selected target not the hit target or the player. This works with any target as long as you can select them.
I tested this in fractals and the heart of the mists.
The damage is not huge, so I dont think its super exploitable, but in PvP especially it could potentially keep people in combat across half a map, so it should probably be fixed.