I've seen a couple of bug report on this issue (MC-81488 in particular) but this is slightly different. Rarely, when I create a new world (about 1 in 20 times), the a lot of chunks within a certain radius of spawn are displaced. These chunks still belong to the biome where they were created (e.g, a chunk created as part of a forest that then appears in a desert will still have the characteristics of a forest biome, like rain and sky color.) This happens without any changes to the world, no log output errors occur, it just happens and I have no idea why. See the attached pictures for examples of this bug.