Instead of Grass blocks in Mangrove Swamps, Dirt blocks are generated if there are any blocks above them (Grass, Vines)

Summary:
Instead of Grass blocks in Mangrove Swamps, Dirt blocks are generated if there are any blocks above them (Grass, Vines). This happened after fixing MCPE-155414 and MCPE-153729.

Seed: 7159122465189192029
Coords: 4645 70 273 
Coords: 4665 64 252

Seed: -732078047
Coords: 1877 63 -910

Steps to reproduce:

1. Create a world with the specified seed.
2. Visit the specified coordinates.

Observed results:
Dirt blocks are generated instead of Grass blocks.

Expected results:
Grass blocks will be generated on the surface (even if there is Grass or Vines on top).

Image: