Unpowered sky facing Piston remains on after pushing Block of redstone

What I expected to happen was...:

With a block of redstone on top of a sky facing piston or sticky piston*,* it should retract after being powered

What actually happened was...:

With a block of redstone on top of a sky facing piston or sticky piston, it did not retract after being unpower. Instead the piston or sticky piston remain extended.

Steps to Reproduce:

1. Place piston (or sticky piston) facing the sky (wood part up)

2. Place Block of redstone on top of piston (or sticky piston)

3. Power piston (or sticky piston)

4. Un power piston (or sticky piston)

4. Notice that the piston (or sticky piston) does not retract