Whenever I opened the new snapshot all of the items in my chests and item frames disappeared

I got hit by this as well after moving to 14w03b. Thank goodness I take a zip of all words before moving between versions, immediately restored and went back to 14w02c for my survival worlds and only use 03b for some testing.

I also experienced this, though I believe that I only lost my inventory/ender chest contents after reverting back to 14w02c after testing 14w03b yesterday. Seemingly not all of my player data was lost as I logged in in the position that I logged out previously and still had the same number of XP levels. Would be very interested in a fix!

Same thing happened to me and I tested it twice
1.I loaded world on 1.7.4
2.Put some items inside chests
3.Logged out and changed version to 14w03b
4.Logged in the same world all items were still there
5.Loaded world again on 1.7.4 -> every chest that was on chunks which I loaded with 14w03b were empty

I also put one chest full of items on 1000 blocks away and didn't loaded those when entered 14w03b every item were still there.

This isn't a duplicate and it isn't resolved. The issue it is linked to as a duplicate has a resolution that does not apply to this report. The solution indicated for the other report is that it is an invalid report because downgrading your game version is not supported. This, however, is a report that a bug happened when upgrading the game version. Unless upgrading is also not supported, the bug is valid. Furthermore, it applies not just to a narrow range of snapshots, but rather to all versions up through 1.7.10 when upgraded to any 1.8+ version. It is still unresolved because no version has yet been released that allows a safe version upgrade for old saves.