My copy of the mission seems to be behaving strangely. Throughout the game I see rectangular solid back boxes that don't seem to have any function and with which I cannot interact The most strange of these seems to be floating in mid-air above the horse in the courtyard. There are what appears to be two nails floating nearby. If I shoot a bonehead arrow at the box, it just goes right through and breaks on the wall behind the box. If I hit a nail, the arrow interacts with it. I am pretty sure this isn't supposed to be part of the mission.