Weird Shadows

My school has window with our school name on it in vinyl letters.

In the morning on a sunny day, they cast a shadow on the wall.

The picture is actually in focus, but the shadow is blurry. Notice something interesting about the shadow. The places where there are holes, like the center of the "o" in community or the "B" in bay are actually darker than the shadows of the letters. Weird.

If you put a piece of posterboard closer to the glass, the centers are brighter like you'd expect. 

As the board gets farther from the window the holes close up and then get darker.