Put the summary of the bug you're having here

What I expected to happen was...:
The bottom piston would have no power so it would collapse and the top sticky piston would receive power

What actually happened was...:
red stone powder went through the piston part and was still activated

Steps to Reproduce:
1. place a sticky piston to the sticky side is up
2. place another sticky piston on top also facing up
3. place block adjacent to bottom piston, place red stone powder on that block
4. place block next to last one and place a red stone torch on it
5. bottom piston should have pushed up top piston
6. place a block next to the piston part of the bottom (placed block should be floating 1 above ground.)
7. place red stone powder on the block and activate it with another block and red stone torch
8. remove the red stone powder on the bottom
9. the bottom piston should be still activated (this is the bug)