Sometimes when I go explore a world in creative mode on 1.7.1 (although it's happened back in 13w41a as well), I'll use the pick block key or scroll to a block (usually one of the new flowers or saplings) on my hot bar. Upon doing so, there's a small chance of every block (whether in the world or in the inventory) turning completely black. It's not easily tested (because it happens randomly), but it doesn't resolve itself until the client is closed and reopened.