You probably have RONA activated. Redirect on No Answer. It's usually found at the bottom 2nd page of the hunt group form. If an agent recieves and ACD call and doesn't answer it after the specified number of rings, the system will put the call back and queue and place the agent into Aux work.
To remove it, you would simply clear the field, but be aware that if it will ring at that phone until someone picks it up.