If a mob is standing on top of a hopper or slab that is the upper half of a block the mobs shadow shows through the block on to the block directly below it, but no further

When I was messing around with hoppers I noticed under the hopper the shadows of the mobs above them were showing up and after that I tried it with slabs. I tested it with the hoppers facing all directions and with different types of slabs. I have also tested it with different types of mobs (Chickens, cows, golems, etc.)