Because of sweeping attack, people have accidentally killed their pets or died by hurting a neutral mob, like an iron golen. Because of the sweeping attack, I have died before because i try to hit something else but I accidentally hit an enderman, and I died from it. Earlier today, I tried to hit a boat with my cat in it, but the cat died as I hit the boat. Here's a bug related to boats and the same issue: MC-169637.

Not only that, but tool cooldown is also a bug with 1.9. This makes it harder to kill things. There's a video on Youtube about the top 5 worst minecraft updates: https://www.youtube.com/watch?v=ER2vEC9lMac&t=1s

 and 1.9 is on that list. Other than the sweeping attack, and the tool cooldown, 1.9 is a good update. Sweeping attack itself isn't that bad, but the fact that sweeping attack can hurt or kill your pets is an issue.