The question is just one out of curiosity, and the object in the render is just a random 3D doodle so to speak.  Lightening the shadow a small amount can reveal other objects that would otherwise be hidden in the shadow of the larger object.  You may be right in that the shadows are behaving the way that they should but it didn't appear to me that way.  The cube object is not hollow.  Where the "windows" are it is a simple inward extrude with intact faces so the object is still solid. In a physical sense there is no real way that the interior faces of the "windows" have either light shining on them or an object that can cast a shadow on them as they are a self contained box.

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