When facing upwards, sticky piston will not retract redstone block

When sticky piston is facing upwards with redstone block placed on top (touching sticky side) redstone button will activate piston, pushing the redstone block upward, however once the current is gone, the sticky piston will not retract. it seems that the extended piston acts to complete the current, preventing the piston tfrom returning to its retracted state

What I expected to happen was...:
I expected the sticky piston to return to its retracted state once the redstone current was no longer activated.

What actually happened was...:
The piston remained in the extended position until redstone block was destroyed

Steps to Reproduce:
1. place sticky piston so piston will extend upward
2. place redstone block on top of piston
3. activate piston with button