3DS Max Dual Quat skinning issues

Where does Max get the data to drive the DQ skinning?

I’m skinning a char whose arms are flat and wide, so twisting causes major collapsing geo. So far I’ve been able to solve it with DQ for the other chars designed the same way. I’ve used the same process on over 40 char without any issue. I skinned the left arm with DQ and it works fine, for for some reason the right side is all messed up. While the skinning is correctly weighted between the forearm bone and the twist bone, one ring of verts that is DQ skinned seems to be getting its information from one of the neck bones instead of the forearm. When I move the head, the verts in the arm move, but they are correctly skinned to the right bones. I double checked in the weight table. Carefully disconnecting the bones, it appears that the head bone is driving the deformation. I can’t understand why, because they aren’t even connected in the heigharchy, other than they are both parts of chains connected to the spine.

Heres a vid of the issue:

Is this a geo issue, or a bone issue? Why isn’t DQ blending using the weights assigned to the verts?

Thanks for any help you can offer.

j