I am in CT and we interped that if the offense sends a 12th man into the huddle, we give them until the huddle breaks before we flag. If the player runs on to the field as the huddle is breaking and the replaced player runs off, thats fine. We note that breaking the huddle with 12 is not necessarily a foul, unless the replaced player doesn't leave the field immediately after the 12th player has entered the huddle.