I loaded up a world from 1.8 Pre 1 and the chunks were all rapidly cycling between what looked like about 5-7 different chunk-types (Taiga trees, hill sections, etc) and my FPS dropped to 6. I tried walking around and it seemed I could still walk properly as if I was on my old world. (I could see my chest and jumped up the hill I knew was there to get to it) This glitch constantly happened every time I created/loaded a world and I also noticed my memory was a constant 98-99% full. I reloaded the game today however, and this glitch has seemed to have disappeared. This means I don't have any screenshots to help out, and I'm not sure if I can replicate it. I figured I'd at least report it so that I'm hopefully able to help decrease the chance of it occurring for anyone else.

If it reoccurs I'll screenshot it and add it in, if possible. Otherwise I'll leave a link to the screenshot in the comments.

EDIT: I would also like to mention this was ALL chunks that I could see, even the sky.