I just started a new world, and there has been some really wierd glitch with the terrain. Centered roughly around -380 130 there was a sphere shaped outline of chunks with completely different terrain. The only terrain settings i messed with was the frequency of dirt/gravel/granite/diorate/andesite spawn rates. Seed: 4235921563217522100

I then started a new world (this time without messing with the spawn rates) and I couldn't find similar glitches, despite doing a 360 with 24 chunk render distance.