Steps to Reproduce:

1. Create a new world with the Caves & Cliffs toggle enabled;
2. Use the "Abandoned Village" seed from the seed picker;
3. Travel to the coordinates displayed on the screenshot.

Observed Results:
The floor is completely flat and fills the cave.

Expected Results:
The floor is water instead.

*Screenshots/Videos attached: Yes

Notes: This is likely related to the mountain biomes.