Scale issue during Transpose Rotation for Animation


I just started doing animations in zbrush to simulate animatronic movement of a Mardi Gras prop I’m developing and encountered an issue when attempting a basic rotation cycle of an arm. The arms and head are separate subtools and I was trying to use transpose rotation to animate his right arm up to as to drink from the cup. I was able to set the keyframes and record values for the rotation just fine, but when I scrub the slider to review the animation the scale of the arm changes as well for some reason, which yields poor results. The scale is affected only the the plane perpendicular to the axis of rotation. I had the same issue with the other arm and head. As a work around, I broke the overall motion down into 3 steps, so the scaling between was less noticeable, but I’d like to figure out what I’m doing wrong or how to fix this.

Thanks in advance,