*What I expected to happen was...:
The piston would deactivate.
*What actually happened was...:
The piston will not go back down.

*Steps to Reproduce:
1.Get two redstone blocks and a sticky piston.
2.Place the piston facing up and a redstone block on the side so it can activate.
3.Next place another redstone block on the first redstone block, then destroy the first redstone block.
4.The piston will stay activated.