Snow creates irregular drop shadows on map

In the picture attached, there are two large squares of snow. The upper square is on top of grass (any solid block works). The lower square is on top of snow layers stacked to a full block's height. There is a drop shadow between the two squares.

The upper square also has one 'snow-on-snow' block in the middle, to demonstrate the point. Note that this does not occur with actual snow blocks.