The bug

It was possible to launch arrows into the air using a slime block and piston. When the piston was activated it would push the slime block up and any arrows on top of the slime block will get launched in the air. In 1.11 this no longer happens.

How to reproduce

1. Put down piston that can be activated via lever, button, etc.
2. Place slime block on top of the piston
3. Take bow and shoot arrows into the top of the slime block
4. Activate piston
   → Most arrows stay on the slime block and do not launch up like in previous versions