The Bug:

The outside bottom walls of mansions don't replace one block with air.

When mansions generate intersecting terrain, the center block above the three cobblestone walls along the outside walls of the mansion is not air.

Here is an example:

Seed: -5727418268269636163
Coordinates: /execute in minecraft:overworld run tp @s 15759.30 69.00 12275.81 708.97 5.85

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look closely at the blocks within the outside wall.
3. Take note as to whether or not the outside bottom walls of mansions replace one block with air.

Observed Behavior:

The outside bottom walls of mansions don't replace one block with air.

Expected Behavior:

The outside bottom walls of mansions would replace one block with air.