Using a spawn egg on blocks less than a full block high spawns the mob too high

The bug

When a spawn egg is used on a snow layer, the mob spawns an entire full block too high, as though the snow layer were a full block. This is a general issue for all blocks that are less than a full block high.

How to reproduce

1. Place a snow layer
2. Use a spawn egg on it
   → Mob spawns one block in midair