Different biomes generate over each other, causing misplaced vegetation and misleading foliage color

Old description:

This was prevalent within the experimental snapshots as well, and has carried over to 21w37a.

Dead bushes will sometimes generate in biomes they aren't supposed to. You can see them in plains, meadows, taigas, savannas, etc.

Though generating in swamps is intended, they seem to do it much more often now.

The bug

With the introduction of 3D biomes, different surface biomes can now generate on top of one another, even when it serves no purpose. In the attached screenshot screenshot-1.png, there is badlands above a plains biome. This can be confusing to players when they build with grass or leaves and notice different colors depending on the height.

This also leads to biome decorations being placed in wrong places. In the screenshot screenshot-2.png, dead bushes from the above badlands biome are being placed down onto the plains biome.

Another side effect of this issue is special ore placement rules (such as abundant gold ore in badlands) break when a different surface biome generates below it (see MC-236705 - where a forest generated beneath the badlands).

Examples

screenshot-1.png:
Seed: 1755992158

/execute in minecraft:overworld run tp @s 260.03 104.50 -1430.19 24.75 39.18

screenshot-2.png:
Seed: 1755992158

/execute in minecraft:overworld run tp @s 308.59 116.65 -1564.51 -135.1 37.1

screenshot-3.png:
Seed: 7591629109323498270

/execute in minecraft:overworld run tp @s 1225.98 100.41 -1265.78 -488.00 58.60