I´m sorry I thought you are informed of this giant and annoying bug. Because of this Bug you are able to attack quite often than you are usually able to. For every click you do the Goblinking or Arwen... Nazgul (on foot) attack their enemies. It´s annoying cuz those heroes can attack faster than it is actually possible.
That would be in their weapon coding. Try playing with the attack delays and such to try to match them with their animations.