I'm using sticky pistons to move redstone blocks to power other sticky pistons and I ran into this bug where the redstone block powered pistons do not retract when the redstone blocks are broken. The screenshots show exactly what I am referring to. Something else that's odd is that the redstone block powered pistons actually retract and extend one time very quickly when the redstone blocks are retracted. A block update is required for the redstone block powered pistons to stay retracted.