When using the "Re-Create World" button to recreate a world that was generated with customized settings, the new world wont have the same biome (if a specific biome was selected in the first place).
Instead of the intended biome, the recreated world will have the biome after the next one on the list of possible biomes.
E.g. Ocean -> Desert, Plains -> Extreme Hills, Desert -> Forest.

Reproduce:
1. Create a Customized world with a specific biome.
2. Re-create that world. The wrong biome will already be in the settings.

I do not know if this bug also affects other customized settings and the biome was just the most obvious one.