Several Hills biomes do not generate sporadically replacing patches of their regular biome counterparts

Several Hills biomes do not generate sporadically replacing patches of their regular biome counterparts. They generate like a completely separate large patch biomes, making them quite rare.

Example:

Taiga generates small patches of its hills biome.

But - Swamp doesn't.

Affected Biomes: (May be incomplete)

1. Dark Forest Hills
2. Tall Birch Hills
3. Giant Spruce Taiga Hills
4. Swamp Hills