I was trying to make a 3x3 piston door so i found a tutorial on YouTube and made it in 1.4.7
It worked normally, but when I tried to turn it on using Snapshot 13w10a, my sand in the middle broke. It only happens when i try to open the door. Whenever i close it, it works fine.

Steps to Reproduce:
1. Open the world
2. Turn it on and notice the sand block breaks
3. The sand block drop will be in the back
4. Go back to 1.4.7 and it works fine
5. just put another sand block in the middle