When I downgrade to 1.7.4 all my items in the world are gone

Put the summary of the bug you're having here

What I expected to happen was...:
Nothing, everything should have stayed the same.

What actually happened was...:
I was in the end and when I relog into the world I would be back where I was a few minutes ago, and I went back into 1.7.4 to fix it and when I got back on all my items, in my inventory, chests, and ender chests were gone.

Steps to Reproduce:
1.Quit minecraft
2.reopen in the snapshot.
3. and look in your inventory and chests.