A new one
I just make top/bottom Fillet
then try Shell middle face...fails...normal ... flip... center line

http://moiscript.weebly.com/uploads/3/9/3/8/3938813/false_thickness2.3dm

Edit! Ok That works only if this object is not a volume/solid but a "surface(s)"!
So effectively kill a face make the trick...but seems that must not be that normally!

When i have a cube i can take a face and make a Shell! ???