When Updating from 1.7 to 14w28b, All Item frames will Disappear and Appear on the ground. Also, There is a HUGE frame rate lag.

To catch this bug:
1. Create a new world on 1.7.
2. place an item frame where ever you want to place it.
3. Save and quit to title.
4. Launch Minecraft with Minecraft Snapshot 14w28b.
5. Open up the world you created and you will catch the bug from there.