Two of Minecraft's biome variants (specifically, the Modified Gravelly Mountains and the Giant Spruce Taiga Hills) are the exact same as their regular counterparts (the Modified Gravelly Mountains is no different than the Gravelly Mountains, and the Giant Spruce Taiga Hills is no different than the Giant Spruce Taiga). To reproduce, create two buffet worlds that use the same seed and select the regular biome for one of the worlds, and the "clone" counterpart for the other world. You'll get the exact same terrain and features, even though the biomes are labeled as separate biomes.