I was in my survival world running 14w03b and I noticed it seemed to be buggy, so I downgraded back to 1.7.2. I then found that my inventory was cleared and nearly all the chests were also cleared.

What I expected to happen was...:
The bug I was experiencing to go away.

What actually happened was...:
My whole inventory and (almost) all of my chests were completely cleared.
The bug did go away though...

Steps to Reproduce:
1. Generate a new world (normal type) in version 14w03a or b. Survival or Creative.
2. Put something in your inventory and/or in a chest.
3. Close Minecraft and downgrade to anything before 14w03a.
4. Notice that your inventory is now empty and so is the chest.