I updated my world to 14w03b to use some of the new features. it was extremely laggy so i switched back to 1.7.4. When i did that, all of the items in my inventory were gone, even my armor, along with all items in item frames. Most of my chests were also empty after this, split right down my storage room, left side empty, right side normal. No idea what happened, but figured it would be worth reporting.