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.
Attachments
Comments 8
made this ticket more easy to observe, simply grass generating under ground under overhangs, in mesa biomes the surface materials are not under ground in certain cases and replaced by stone.
Edit: also fixed a typo
I made a further edit explaining that this was "fixed" in bedrock edition, and I also greatly summarized the bug report while making it more specific.
Edit: It turns out that the bedrock edition "fix" is actually a bug, but still. snow, podzol, and grass should not generate under overhangs.
I can confirm this behavior in 21w37a, but I'm unsure as to whether this is an issue or not. You can use the following seed and coordinates to reproduce this in 21w37a.
[media]Steps to Reproduce:
Enter the following seed and coordinates.
Seed: -59145707969391316
Coordinates: /execute in minecraft:overworld run tp @s 21884.44 102.56 577.34 252.21 28.54→ ❌ Notice how surface blocks generate under overhangs.
Please clarify the bug report, explaining what happens vs what you expect to happen. As-is, it is very unclear.