Hi oldaviator.
To answer your question, aerial photos are very small.
They are pieced together nicely to look like 1 giant pic, but they actually many small ones.
So most likely the shadows are out of the pic, and when the next pic was taken the shadows either werent there or moved.

Look at the aerial data just offshore in Maine. Here you can clearly see each small aerial picture and their average size. Because of the moving waves and water texture, its impossible to make it look like just 1 pic.