Surface blocks generate under overhangs

The bug

Surface materials like grass blocks, mycelium, podzol, and snow blocks (depends on biome) will generate under overhangs. This is a bug because it looks really weird to see these blocks generate in places where they shouldn't be.

How to reproduce

Use the seed 96, /teleport 9094 112 8523, to see grass in a dark place where it shouldn't be.