For some reason, chunks glitch out when you exit a world and reopen it. The first time you load a world after opening Minecraft, everything is fine. The fun starts when you reopen the world without closing the game.

Reproduction steps:

1. Run Minecraft snapshot 15w42a.
2. Create a new world or open an existing one.
3. Exit to the title screen.
4. Reopen the world.

I attached a screenshot showing the problem.