LateUpdate override of bones in Mecanim Animation not working

Unity 4.6 b17

I have a mecanim animation (Generic) playing on the model.
I have a script placed on the neck bone as I wish, occasionally to take over control of the head.
In the LateUpdate() of the script I set as a test

transform.eulerAngles = new Vector3(00,180,0);

what i would expect in this case is the head angle to be rock steady in world-space, however the rest of the animated parts moved…
what actually happens is that the code affects the head but it still wobbles about and rotates slightly here and there - affected by the animation.
When the animation is turned off it behaves perfectly.

all the answers I’ve searched seem to suggest that LateUpdate is the answer but it’s just not working for me… Anybody got a clue for me?
Animate Physics is not turned on…
thanks a bunch.

You can try avatar mask, it will allow you to do the same you expecting for.
Avatar Mask

Does your script use a smooth factor for the animation? This was an issue for me…
The mask also did nothing for me, it seems the mask, does not truely mask the bones, but instead the animation is applied to all bones and then masked… If that makes sense? I’m away for a week, but if you can’t solve it by then I will take a look at my code when I am home and see how exactly it was solved.