shell on surface with nurb-edges (to make a surface solid)

 From:  flashnfantasy
i loft it with straight, just to test, that is a problem of mixed straight and round.

the picture below shows an offset with a bigger number, all edges are straight.

the offset surfaces are misaligned, but obviously the programm tries to handle them as if they fit together.

you also see, this problem does not only occur on open edges.