If you have villagers in 1.7 or before, and then load that same world with 1.8, the villagers will corrupt the chunks
Steps to Reproduce:
1. create 1.7 (or before) world
2. Find villagers and do some trading
3. Update that world to 1.8
4. place blocks near villagers and reload world.
5.blocks will be gone due to corrupted villagers corrupting the chunks in that world
Cannot Reproduce
If world was opened with snapshots between 14w25b and 1.8 pre1: Won't Fix. Restore a backup from pre 14w25b.