have you tried actually attacking the nearest mob?
have you tried giving the kill command again and healing the pet so that it doesn't die?
I will leave this here, for now. But I'm not sure there's any bug here, rather a misunderstanding of the intended function of autodefend.
Regarding warrior defending - it is a problem i encounter a lot doing spawns. I use a swordsman and whirlwind - but in heavy spawn, if you are in war mode - it will wait for you to pick a target. Even if you take damage from the nearest mob, it will not fight back. While, you not in war mode - it works most of the time, until some mob cast a spell from away and u are suddenly out of range for defending, wich for me is a lethal situation.
When it comes to pets, thats a different story. I will try to explain them here;
1. If your pet fights something and is targetted by something else - it stops fighting. You have to give commands over and over, and preferly say 'all stop' then command it to kill again - that works for a while. Try go to fire island temple, stand at top with a pet and fight the deamons - once it get targetted from downstairs, it takes many commands to get it to fight, even at 120 tame/lore.
2. If you fight with you pet, and you command it to fight a monster (and as for the leader of it, i would love to decide what order to kill - as it worked before), it will turn target once it is targetted and fight other stuff - or just run off try to get to it, instead of continue the battle it is ordered to. Example for this will be a t-hunt spawn or other spawn with different mobs, and you want to take out the highest threat monsters first as a poison element or ancient wyrm - it will not listen to your commands once it is targetted and fights as it wants - the AI for this is not working any more.
I have been a tamer since 98, and fought a lot of battles with my pets - now I cannot rely on them or have them as an assistant in the battle. I will more often risk to die to save them instead, because the commands that are give - is not followed.
With this I mean; when a pet is ordered to attack monster A, it should concentrate on the command - not run around like a maniac to hit a hidden rat behind a wall, or something it cannot reach. Even if it is multiple targets around, it should stay at the command. The 'all stop' command works, but once you tell it to fight again, it will listen for a few seconds till its targeted again. And by all means - when something is making damage to it, it should auto defend against it as long it is not told to stop and follow the owner.