Put the summary of the bug you're having here

What I expected to happen was...:
I expected nothing to happen

What actually happened was...:
Piston extended

Steps to Reproduce:
1. Put a piston to extend vertically.
2. Put earth on piston
3. Put redstoneblock on earth (see pic1)

4. Remove earth and the piston gets extended (see pic2)

Same problem if putting the redstone first without earth into the air and put the piston next with getting no contact. (Pic3 and Pic4)

Works only with both types of pistons not with other redstone components like redstonelamps