If you generate a world in Buffet with Floating Islands will generate some underground structures exposed to the void

What I expected to happen was...:

It should generate neat islands

What actually happened was...:

Some structures will generate in the air.

Steps to Reproduce:
1. Create a new floating world by using Buffet and make sure Generate Structures are on.
2. Use /locate Mineshaft or /locate Stronghold
3. Teleport to the location. If the structure is near the edge of the island it will be exposed