I don't understand the reason why this happens, thank you in advance for any helps:
This is a simple rigged and skinned character with an FK setup for the Arm.
(copy and paste the link on the address window to see the images)
I've applied a BlendShape and a Set Driven Key in the way that when the elbow rotates, the bicep muscle expands (the blendshape value switch from 0 to 1), and the elbow area doesn't lose volume.
The problem arrives when I rotate the shoulder (or any other spine or hip bones) forward and backward (also up and down)
You can see that the elbow area continues to deform also if the rotation value of the Elbow_joint remains fixed.
I have to say that creating the BlendShape I've used a "Parallel" Deformation Order, and maybe this could be the reason, I don't know; I've tried using a "Front of Chain", and it seems to work better, but I've to deform the target geometry in a strange way to obtein good result.
Anyway. Any explenation or advice will be well accepted.