Sticky Pistons will sometimes remain powered without a Redstone signal of any sort. Not referring to Quasi Connectivity or anything like that. This is a Sticky Piston, floating in midair, that remains powered. What made it particularly strange was that the Sticky Piston in question extended the moment I placed it, before it had even received a signal, but another Sticky Piston in practically the same situation did no such thing.

What I expected to happen was...:
I thought that the Sticky Piston would retract. I didn't do anything special to it.

What actually happened was...:
The Sticky Piston remained powered despite floating in the air without any blocks or Redstone input triggering it. 

Steps to Reproduce:
This issue occurred while recreating the armor stand cycler from one of the Redstone guidebooks, if that helps at all. I also did this against a wall, but even after removing the wall and rebuilding it a few times, the issue kept happening.

1) Place a Sticky Piston face-down.

2) Place a Redstone Block on the sticky side of the piston. 

3) Leave one block of air below the Redstone Block. 

4) Beneath the air block, place another Sticky Piston face-down (this one is the one with the problem). 

5) Just like with the first Sticky Piston, place a Redstone Block on the sticky side of the piston. I've gotten this issue to happen without this block, but for the sake of being thorough, I've included it.