Visual World Glitch

I start up a world on Minecraft, right after I've launched it, and it's perfectly fine, but if I don't like the generated world and I got to make a new one all I get is a ton of random blocks being placed all around the screen. I can move ad there is a terrain, but all I see is constant blocks randomly jumping all over the screen. If I ever make a Creative World the same thing happens. This only happens in the Snapshots for 1.9, 1.8.9 and under doesn't have this problem.