Non existing mob and weird character behaviour (video)

Judgedread101071

For quite some time now I've noticed that my character especially in boss fights with adds, has ben acting weirdly.When for exmple i tab target the boss and turn my back to him and then try to hit an add,in many occasions my char just ignors what is in front of him and turns around to hit whatever i have tab targeted.And if the tab targeted mob is out of range, then i get stack in a heavy attack animation.You can clearly see in the video that although there is nothing in front of me the UI "sees" the tab targeted add at a specific location!!!!! And when I try to hit the non existing add then the char turns around and hits the actual one!!
https://www.youtube.com/watch?v=s1o8h8HfqPM&feature=youtu.be