Not sure if bug or fix, but I don't like it, it will break many redstone builds or make them take a much longer time. Sticky pistons don't leave the block out if they receive a 1-tick pulse.

I expected the sticky piston to leave the block there.

The piston retracted and pulled the block back.

Steps to Reproduce:
1. build mono-stable circuit with piston attached to output
2. power the mono-stable circuit with a button or lever
3. observe that the sticky piston keeps the block when it previously didn't.