Piston bug. Rather than documenting it, I hope you don't mind a 55 second youtube video. https://www.youtube.com/watch?v=V1wnXWGwcc4
I got another example. It happens on both 1 and 0 tick delays, it seems.
https://www.youtube.com/watch?v=Kam-8QCi3Lo
Sorry if this is a clone, just there are so many issues out there it's nearly impossible to know.
Linked issues
Comments 4
Ah, thanks.
But duplicate of MC-1230
Fail to see a bug here. Please describe it with words.