Weird scalp mesh shadow in Iray Interactive

Diaspora

Models used: Genesis 3 Base Female and Misty Hair with Iray 10 Misty Hair material

The first image is made with iray photoreal, the second is made with iray interactive, in which the misty hair scalp mesh is still casting a shadow even though that portion is supposed to be transparent to the point of invisibility. 

I've tried a bunch of different render and material settings but can't make that slight shading completely vanish. Even turning the cutout opacity all the way to 0, that shadow still is there in interactive. The only thing that makes it disappear is by using the geometry editor to hide the scalp polygons. 

Is there any way to fix this?