It's an optical thing that seems to happen when the light comes from the bottom of an item instead of the top. Your brain sees the shadow in the wrong place. If you stare at both sides they will both go to a recessed mold to your eye. it might take a few seconds but, you'll see it happen.
Look at the attached photo especially the chip on the left. If you stare at it and then just look slightly off center it will appear to go from incuse mold design to a protruding one.