I am trying to rig a first person set of arms, but the bones in the forearm are acting strange. I made three bones parented to the large forearm bone, they have copy rotation constraints linked to the hand IK bone so that they will only copy its Y rotation. It works in the rest position, but after moving the hand IK bone and rotating it along other axes, it doesn't follow correctly.
Here it is working fine.
After repositioning the arm, it does this. It barely reacts to the hand Ik bone rotating along the Y axis, and instead reacts the the Z axis.