While building a flying machine I noticed that under certain conditions my piston does not pull back the slime/honey block in front of it. I broke it down to the constellation that you can see in the first screenshot (2020-10-04_19.45.22.png). The second screenshot (2020-10-04_19.45.39.png) happened after flicking both levers. The third and last shows what happened after turning the levers back of. As you can see, the slime blocks in the middle of the bottom contraption are not pulled back, and I can't really think of a reason to why that is, so I decided to file a bug, as this doesn't seem right to me.

If there's an actual reason behind this, then I'd be happy to know! Thank you.

Note: I'm playing a modded version of Minecraft, but this behavior is also reproducible in the vanilla version and the newest Snapshot of the game.