Terrain fails to map beneath a structure

**Describe the bug**
Terrain in the overworld fails to map under structure sprites that appear in a specific configuration.

**Affected biome structure sprites**
While several configurations are possible, only the two that currently in use are listed here.
black: swamp_forest2 (swamp_ruins)
green: forest2 (lake)

**Affected configuration**
The issue occurs when the Wave Function Collapse when a tile of the overworld uses a configuration of the four tiles that represent the center of a structure, shown below in green.


**Screenshots**