I had this problem as well - similar to a "face-fighting" kind of artifact where the software can't decide which face takes precedence, except with a shadow. When the "sun" is coming straight across a face, the software can't decide whether to show it shadowed or not (thus this artifact).
This shows up on Face-Me components because as the camera travels around the model (if it is roughly 90 deg. off from the sun position) the Face-Me component is rotating to face the camera, and at some point it will become perfectly parallel to the sun's rays.