I found that when I have a torch, sapling or mushroom in my hot bar, and then scroll over that item, all the blocks in the world disappear and all remaining features flicker rapidly. I'm only able to view mobs, lava and the wire cube that would surround a block. I'm able to mine items, I just can't see what they are. When I scroll off of an item listed above, the flickering stops, but the blocks are still missing. At this point if I open the options, choose resource packs and then back out, the blocks all return. I have no mods or packs installed, and this only happened after updgrading from 1.6.4 to 1.7.2.