Parts of the world don't render textures but have physics
Any world opened OR created on 14w25b/a looks normal to me until I fly/walk out a little bit, once I get about 4 or 5 chunks from my spawning point, the world begins generating 'phantom' blocks, not rendering their textures but their physics remain the same.
If you place blocks in the 'phantom' area, they too don't render their texture but still have physics. If you set up some sand in the phantom area and make sand fall, the entity still appears but no change happens after it lands and becomes a block again.