Put the summary of the bug you're having here

When a sticky piston pushes a redstone block directly into the face of another piston above it, and then tries to pull it down, it gets powered by that redstone block and gets stuck in the powered position.

HOW TO REPLICATE:

1. Place a piston facing upward, with redstone block on its face
2. 2 blocks above it, place a piston facing downward so that its face is facing the redstone block (but the face should not touch the redstone block)
3. Power the bottom piston (maybe using a redstone block)
4. Unpower the bottom piston