Question about KB

I hunt HH a lot when I'm bored or want a few % but don't feel like training. Usually when I find one all I have to do is Bullseye and hold Cannon for about 90 seconds, and he'll stay in the same spot and die.

Sometimes, I'll have a low level ranged class ask me to kill one for them. I don't mind, they usually save me the trouble of searching a few maps and HH doesn't really have any rewards I care about. When I fight one with them, sometimes HH will break free of KB and I have to move back a bit and set up Octos. I'm still hitting HH at the same pace and all of my hits KB, but somehow the additional non-KBing hits screw things up. Why is this?

This is an age old mystery. Seems your low lvl friend has somehow taken dominance over the monster instead of you, and since the server only pays specific attention to one user vs. the monster, your KB effect will mean nothing. It's the same case as Warriors rushing monsters or Buccaneers screwpunching something.