Doubt about bone orientation in a biped rig

After doing my own rig, after watching the Humane Rigging DVD, I got an issue. Then I confirmed it on other rigs I got from internet and finally even on the “mr_biped_rig.blend” rig included in the DVD.

Here the problem, using Mr. Biped rig: http://www.pasteall.org/blend/13625

I posed the Right IK hand, copy pose, flipped pose, I-LocRot for both hands, for a resting pose(frame 20).
Then I posed the hands like Mr. Burns( frame 50).

Everything seemed right, but the resulting animation was obviously wrong ( from 20 to 50 in the file).

I fixed it in an easy way negating the values of the Y and Z axes of the quaternion of the final pose (frame 150).

Finally I’ve tried the rig generated by the rigify add-on and the animation works fine! But then I noticed their bones have a different orientation. Their local Z is towards world Y negative.

So, Is this the proper behavior? Or Is it a bug of the “pose-flipper”? or something else? Is a must to orientate localZ->-worldY in the IK bones?