Underwater in mangrove swamp biome generate grass blocks

Summary:
Underwater in mangrove swamp biome generate grass blocks.

Seed: 7159122465189192029
Coords: 4601 60 331

Steps to reproduce:

1. Create a world with the specified seed.

2. Visit the specified coordinates.

Observed results:
Underwater in the mangrove swamp biome, grass blocks will sometimes generate.

Expected results:
Grass block will not generate underwater.

Image: