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:
Version: 1.19.4
Seed: -5727418268269636163
Coordinates: /execute in minecraft:overworld run tp @s 15759.30 69.00 12275.81 708.97 5.85
Steps to Reproduce:
Generate a world with the seed provided above and teleport to the given coordinates.
Look closely at the blocks within the outside wall.
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.
Linked issues
Attachments
Comments
Can confirm in 20w51a. Can be seen with almost every mansion so provided seed + coordinates isn't necessary.

There are mansions which do not generate through some hills, it's better to have them, and not need them, than to need them and not have them.
Relates to MC-107916.
Can confirm in 21w03a.
Can confirm in 21w16a.
Can confirm in 1.17.
Can confirm in 1.17.1.
Can confirm in 1.18.2.
[media]Version: 1.18.2
Seed: 5674588914129534515
Coordinates: /execute in minecraft:overworld run tp @s -3482 105 3034 83 35

In 22w15a
Can confirm that this is an issue. Also affects 20w49a.