vanilla_layered biome source type in buffet worlds ignores biome options

When a buffet world's biome_source/type tag is set to minecraft:vanilla_layered, the game ignores the contents of the biome_source/options/biomes tag and generates the world with all DEFAULT world type biomes. This is especially visible in the latest snapshot if the biome_source/options/biomes tag only has nether biomes.

How to reproduce:

1. Create a buffet world.
2. Exit the world.
3. Open the world's level.dat file and change biome_source/type to minecraft:vanilla_layered.
4. Add nether and/or end biomes to biome_source/options/biomes and delete all overworld biomes.
5. Delete the region folder.
6. Enter the world.

What I expected to happen was:

The world would use the biome options to create a world that looks like default but with the biomes I had set.

What actually happened was:

The world ignored the biome options and generated a world with all default overworld biomes.