Currently aggro for any ranged class is bugged, this is due to the spell traveltime interaction with the mob.
What happens is that when you finish casting an attack/spell that has travel time, like Wrath or Cobra Shot, the mob instantly aggro's you and starts running towards you WITHOUT the spell that you previously casted hit him.
What should happen is that when you finish casting an attack/spell that has travel time, the mob should only aggro when that spell has hit him after the travel distance rather than being aggro'd instantly.
Attached come 2 examples with my 1337 paint skills. The second one is what happens, you cast a spell and after casting the mob gets aggro. First one is what should happen, you cast a spell and after the spell hits, the mobs gets aggro.