Working on a Deformed Shell Body

I import STL of deformed shape of shell body from Mechanical to SCDM (SpaceClaim Direct Modeler). Why can't I get a good STL when shell thickness is turned OFF? 

When you turn off the thickness, the two skins of a shell body simply collapses. That means there are still two surfaces of a shell but zero gap between them. Due to zero gap, these STL elements of the two skins get connected which makes it duplicate elements and intersection.