I believe the "pets forgetting their attacker" problem was introduced with the OOC changes which made an NPC forget about you 30 seconds after you left its awareness range. Since pets are NPCs they are also affected.The full thread is here.
We've added a check to exclude PC pets from this calculation which should return them to their previous behavior. Barring any problems, this should go out with the expansion patch.
Rashere, EQ Lead Designer
Sunday, February 11, 2007
Pets - "Thanks for the Memories"
A bug was introduced wherein pets would forget the NPC they were told to attack. This is due to be fixed in the next patch (February 13).