We've noticed that when a player is on a quest that requires them to kill certain mobs and things, when a pet (of any kind) gets in the last hit, the kill isn't counted towards the quest.

Would you be able to fix this? If a player his the mob, and the mod dies (killed by pet or another player) that player should get credit.

I found this to a problem where I've set up a boss-like quest, when multiple players reach the boss stage, only the player who gets in the killing blow will receive credit for it. Which is quite troublesome as this boss only spawns on an event that the players have already triggered.
And since that is the case, they must wait until someone else triggers the spawn event to try to get the killing blow yet again... It's become quite a troublesome loop of fighting over who's going to kill this boss this time, or the player's pets "stealing their kill".

Considering we use MyPet on our server, this is very troublesome for everyone. Everyone uses a MyPet and if they can't beat that pet to the kill, they're stuck finding another mob instead to hope to try get that to count. :
Even MC's normal wolves are causing this issue, btw..