Animation not coming through for additional weapon bone attached to hand

I have a humanoid character that has an extra bone as a child to the Right Hand bone which I use to handle the animations of the weapons. The character has the bone in Unity and is in the right place in the avatar hierarchy, but the transform of this bone doesn't seem to ever update/change values during the animation. Is there a setting that must be configured to update non-standard humanoid bone transforms during animation? I am animating in Maya and exporting as .fbx. All other bones seem to update properly.
Any info would be greatly appreciated!
Thanks.

 

Any ideas what might be going on here?

 

Still scratching my head here.. Has anyone ever used a bone for weapon rotation? is there anything special to do to get the transform updates to come through?