Bone tool and child - thing

I noticed a weird thing.

I have an arm and I use a boon tool on that one. works fine.
I have a child layer to the arm which is a hand.

But when animating the hand rotating etc it behaves very strange. I have animated with parent/ child structure before and it worked fine but I does not seems to work so good when you mix bone and child layer.

Any tips on how to do this the best way?

/ Mattias
using Harmoney Adv