The error you are seeing has something to do with the pathing mechanics that blizzard uses. Sometimes when a mob is moving and you iwt on it the click to move is actually targetting a random pixel in the up and down axis. Since there is technically no way to path upwards when this happens they tend to run off toward that pixel but because its in the air they basically start autorunnin to a spot way off in the distance. When you spam iwt quickly with mobs moving you get this more often because the server has a hard time picking up where the click was. Can't be helped and I'll take it the way it is vs the way we used to have to melee box, that's for sure!