The  minecraft:subsurface_builder  in custom biomes will overwrite the surface terrain of original biomes.

If a custom cave biome uses the  minecraft:subsurface_builder  component, and uses  minecraft:replace_biomes  to replace a vanilla biome, you will find in-game that the cave biome with  minecraft:subsurface_builder  spreads onto the surface.

As a result, surface blocks are replaced with stone.

Steps to reproduce this bug:

1. Create a custom biome, add the  minecraft:subsurface_builder  component, then use  minecraft:replace_biomes  to replace a non-cave vanilla biome.

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2. Enter the world, use the  /locate biome  command to find the ID of the biome with  minecraft:subsurface_builder .

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3. Teleport to the coordinates found in step 2.

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4. The bug is reproduced: the entire surface turns into stone, instead of only generating underground.