I created a new 1.8 creative world and changed some of my video settings and all the chunks around spawn started rapidly generating the same chunk from all the biomes. The speed seemed to increase as I increased the mipmap levels.

Found it really hard to explain so I made you a video that shows you everything I know about the bug and the situation.

Video: https://www.youtube.com/watch?v=1AggsqGGDj8
NOTE: Some screenshots in the description.

EDIT: I restarted my computer and tried it again. The issue seems to appear whenever I turn render distance up. This time I tried 8chunks and the result should be seen in the attachment screenshot. It seems like giant friendly mobs were spawning in the middle of that nonsense. The affected area also changes according to the render distance.

EDIT2: It also seems that whenever I restart minecraft it works at first but if I change my settings while the world is open, it starts again. This also doesn't occur on any older worlds but is an issue with every new world I create.