I've had the same problem. As someone else suggested, try putting the noharm check in to stop the macro if you do not have a mob targeted. Not sure if it works as I haven't played my warlock duo for a while.

[code:1]/assist Dujo
/stopmacro [noharm]
/petattack
[/code:1]

I think this has to do with the way pet targeting works. My rogue got very frustrated at hunter and warlock pets knocking us out of stealth. When the hunter or warlock lost their target the pet still retained their target.

I think they changed it at some stage but it is a very buggy area. Combine it with /assist lag and you have an imp that goes AWOL every time you hit /petattack and make new friends.

On my rogue I hated it when I rezzed in WSG GY only to have a hunter send his pet from the other side of WSG and even though I stealth the pet would continue pursuing me. If I remember correctly they put a range limit on /petattack but it was still extremely annoying. Was quite a while ago, not sure if there were updates since then.