I took a vanilla woodland mansion, and turned it into a custom nested structure to generate in my spawn town. I have all the structure voids placed in the correct places so that the inside of the building will be filled with air.

When I generate the structure on land, or underground, everything works perfectly. However, if any part of the structure is generated underwater, blocks like fence posts, stairs, and glass panes become waterlogged. After a few moments the waterlogged blocks update and flood the hallways.

What I expect to happen is that those blocks spawn in their original, non-waterlogged state.