I've done another render and had to increase IC to get rid of the dark smears.

For this render I had rotated the figure approx 90 Deg Y axis to get a profile shot.

So based on very limited data at this point it seams as though there is a correlation

possibly between camera angle and the degree of dark marks. The dark marks appeared on the forehead in the previous render, with the forehead roughly perpendicular to the camera image plane. Second render (profile shot) side of nose was roughly perpendicular to camera image plane and thats where the marks occurred. However there were plenty of other surfaces that were perpendicular to the camera that did not exibit this anomaly.

So there seems to be a correlation, but not consistently so, so I'm not really sure what that tells us at this point, except that playing with IC settings may get rid of it.