I was messing around with minecraft "airplanes" (slime block and piston moving things) and when my ship hit my world barrier the slime block and sticky piston went inside each other. (I was in my private minigame server vanilla) and I DID not photoshop.

Steps to reproduce problem 1. make a flying slime block machine like mine ( this youtube video should tell you) http://www.youtube.com/watch?v=X393TelG0mQ
2. activate the machine and slam it into a world barrier, make sure that the side with only one piston is slamming into the world barrier.
When this effect happens when you try to break the piston it will not break and will stay there, but the slime block will break.
You also can not place blocks on the piston, you can also go through the piston as if it were air.