The Bug
When a cat sits down/stands up on a chest that has items in it and that has a comparator measuring its contents, the comparator does not switch on or off immediately, only when it receives a block update.
Steps to reproduce
1. Place a chest with a comparator facing away from it.
2. Put any item/items in the chest so the comparator turns on.
3. Place a tamed cat on top of the chest and enclose it so it does not run away.
4. Right click the cat so it sits down.
Notice the comparator stays on.
5. Place a block next to the comparator.
Notice the comparator now turns off.
The same applies when the cat is already sitting down and is right clicked again to stand up (then the comparator does not turn on).
What I expected to happen: The comparator updates as soon as the cat sits down/stands up.
What actually happened: The comparator does not change state until it receives a block update.
This bug affects some types of redstone machines, especially remotely activated ender pearl stasis chambers.