Auto shot is bugged when you move. While kiting and you use Arcane Shot, it should enable Auto shot automatically, instead it turns it on and instantly disables it. It's like this for every spell while moving only - when you kite someone or let's say Viber sting a player "while" moving, and you then stand still to start shooting, Auto shot will be turned off. Which means you gotta press it again.
When you use a spell while moving as a Hunter it should automatically set Auto Shot to "auto" so to say, so that when you stop moving Auto shot will be fired instantly.
This seems to have happend right after the Dire Maul North Tribute fix (to stop hunter's from farming gold there)