Can you find the "mistake"?

Can you find the error in this stained glass at St. Mary's?
It's of the fifth Joyful Mystery of the Rosary, the Finding in the Temple.

Now, since it's depicting the time of Christ, long before any of us were around, a rational person would believe that no modern person would have been present. However, as a Lutheran company was contracted to design and create the stained glass for the Catholic parish, they must have hired Doc Brown to transport an Augustinian monk in the d'lorean time machine back to 12 AD. See the little man in the black robe in the upper left hand corner?

It's none other than Martin Luther.

And it wasn't discovered until long after the windows were done and complete. Little stinkers.