Only shells part of a part

I have a part made of a lofted extrusion and a boss extrusion.  When I shell the part SW only shells the boss extrusion, it doesn't shell the portion of the part made from the lofted extrusion.  Any ideas what it is doing, or if I am missing a setting?  I'm only specifying shell and a thickness, I didn't give any removed surfaces or modified thickness surfaces.

Thanks - Greg

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