I received another response from SmithMicro, concerning my "sketching" image.  They told me that polygons from the V4 figure are intersecting with the gown in frame 1.  I don't see it, and I that response makes me wonder about the purpose of draping.  In the attached image (rendered quickly, with stock lights--please don't complain!), the HMann T-shirt on my Brenna figure didn't completely cover her bosom until something like frame 24 of the simulation.  So, if draping permits the cloth to cover intersecting polygons on THIS image, why not on the others I've done?

I don't really understand what the deal is in this situation.