Generated a checkerboard pattern of alternating superflat and default chunks.

1. Start a superflat world on any gamemode. Use any seed, for example "i dont care"
2. Wait for the world to load.
3. Save and quit.
4. Go delete that world.
5. Make a default world with the same name and seed.
6. You will see both default and superflat chunks.

*NOTE: This also works if you make the default world, then the superflat one. Works on all versions. Works only on PC.