Here is a .blend file I've created to illustrate a strangeness I have observed with blender's Inverse Kinematics solver.
Example 1 has an IK and the pre-yaw bone has no IK rotation restrictions.
Example 2 has an IK, and the pre-yaw bone has locked X and Z rotations. Unfortunately, it locks the rotation to pre-yaw's parent bone, even though Inherit Rotation is not checked.
Example 3 is posed without IK at all and illustrates the effect I am trying to accomplish. The pre-yaw bone is correctly vertical, modeling the mechanics of the monitor arm.
I think the IK solver could be enhanced to obey the Inherit Rotation checkbox. It could also be enhanced to obey the Copy Rotation constraint (which exists but is muted since it shouldn't be necessary).
Have I discovered a shortcoming in blender's IK? Is it worthy of a bug report?
How do I work around this weirdness?