Redstone bug

What I expected to happen:
That piston didn't retrieve. It should've retrieved, the one with the redstone block, the other in horizontal position works fine.
What actually happened was:
I was just on a server chillin' out, then I go to the creative world, build a redstone circuit with two sticky pistons, one was in horizontal position, one was in vertical position. The one in horizontal position works fine, while the one in vertical position won't retrieve itself.
Steps to reproduce:
1. Place one sticky piston in vertical position
2. Place a redstone block in the sticky thing
3. Power up the sticky piston
4. Remove the redstone torch or any power source connected to it
5. The sticky piston won't retrieve.