Note: this can happen more with mapmakers.

sometimes when i switch to older versions of minecraft from a snapshot, (ex:14w10b to 1.7.5) all items from everything including player inventory is gone.

also if you switch to an even older version of minecraft after this glitch, some chunks of the world are gone too.

Steps to Reproduce:
1. play on a snapshot from Feb 2014 or beyond
2. switch to 1.7.5 and play on the same world. (there's a good chance it will happen).
3. then switch to 1.5.2 and there should be a chunk of your world missing.
4. if the glitch does not happen, then repeated use will guarantee damage to the world if above procedures are performed.