The Bug:

Grass blocks located two blocks below dark oak trees aren't converted into dirt when the world generates.

Here is an example:

Seed: 1359968930092793278
Coordinates: /execute in minecraft:overworld run tp @s 2794.66 67.14 78.35 233.39 5.55

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look at the grass blocks closely.
3. Take note as to whether or not grass blocks located two blocks below dark oak trees are converted into dirt when the world generates.

Observed Behavior:

Grass blocks aren't converted into dirt.

Expected Behavior:

Grass blocks would be converted into dirt.