On the Customize World Settings Page 1 of 4 there is an option to choose a fixed biome. In a previous snapshot this worked correctly but now when choosing one and clicking done, the slider changes to a different biome. This doesn't affect every biome type.

For example, the slider will remain on Taiga or Swampland when choosing either and clicking done. But, choosing another biome like Cold Beach and clicking done will cause the slider to change to Birch Forest. This can be observed by either creating the world (which will generate the wrong biome), or just by going back into customized settings (the slider will not be where you left it).