I didn't think about it until now, but that shadow from the walls is also wrong; Since those are pyramid shaped walls you'd expect that the 45 degree shadow lines would not be parallel (I don't really feel like doing the precise math, but as an example the shadow on the top left part of the pyramid should be at a 30 degree angle and the bottom right at a 60 degree angle.
This is because the corresponding corners of the pyramid aren't parallel (they are sloped towards each other).