Fligh- thanks for the suggestion. I always forget to do that. However in this case RecalcNormalsOutside (Ctrl-N) doesn’t have any apparent effect- the distorion still exists.
But there is a workaround: Do SetSolid | SubSurf 1 | Convert object to mesh | RecalcNormalsOutside | Set Smooth
Now it has the same level of smoothness and polygons without the distortion.
What’s strange is the distortion was only on the left right jaw area of the head. Not on the left jaw area. So I must have screwed up somehow I just don’t see it.
one more suggestion: make sure you don’t have extra inner faces/edges joining the flipped vertices. the flip sides get stretched out onto the outer surface when you subsurf. so the stripe appears only when you have both subs and smooth on (just had this problem recently too)