Weird Bone Interpolation during Pose-to-pose Animation

The video is self-explanatory, but here is some additional info:

• The poses are, as can be inferred, in the pose library.
• I think the problem is this: When I saved hand-on-hip pose, I only saved upper and lower arm bones, which only saved the transformation of those bones and not the hand itself. So, during interpolation, hand naturally interpolates to default standing pose.