I am having trouble with the Longest Day achievement, where I have to fight so many trainers in a day. Some trainers won't fight with my main (a horde). I was able to get the battle with an allied toon but the achievement only reflected single toon, not account wide. That is, what I defeat on my ally doesn't show up on my horde main, and what I did on horde doesn't show up on ally.
I used to be able to fight them all before I transferred server.
Is there a way to make the trainer behave better? Or is there a bug somewhere?