Updating to the latest Spigot build has caused some sticky pistons to no longer retract blocks. This is a new issue caused by one of the latest builds (pistons acted normally in the build I was using that's a couple months old). From initial testing it seems to be locationally based on the z axis (not 100% sure this is always the case though). Here's a very simple setup that shows the problem. No 0 tick pulses, no buds, just a lever next to a piston. (doesn't retract the block)