Mistakes like these have appeared in the past too, on the Playpeole Knights Superset 1710 the flag on the pole is upside down, so you can see an upside down cross on the front box image. Also on the Doctors and nurses superset 1740 the nurses red collars are on back to front so that the opening is at the back.
Maybe it is deliberate?!! Is it possible? Some sort of secret joking or challenge?