When an item is placed in a chest in 1.7.4, and then the player attempts to move items to/from a chest while in spectator mode, all items in all tile entities in the world are replaced with minecraft:X:None (X being whichever item was in that slot), which disappear when the chest is opened.

Steps to Reproduce:
1. Put items into chest in 1.7.
2. Open world in 1.8 snapshot.
3. Go into gamemode 3.
4. Attempt to move items from chest to inventory or vica versa, shift clicking may be the trigger.
5. Return to 1.7, and open ½ of chests.
6. Check chest contents with MCEdit or similar.