1. If a party member enters combat and you are not being attacked the pet will enter combat. This should not happen. The pet should only attack what is attacking its master.
2. When you use a breakable CC like a stun the pet will immediately attack that target and break the CC. If you attack a mob first then CC another mob the pet will still likely attack the CC. NPC companions do this as well. This should never happen.
3. When you die, resurrect and summon a new pet that pet will immediately attack the mob that killed you. This should never happen.