In the 11/1/16 V6 WIP, clipping planes sometimes clip away more (or all) of the wireframe of an object then they should.
As an example, create a cube in positive x-y-z space with one corner at the world origin. Create a clipping plane in say the rhino x-y plane, with its “keep” direction pointing in positive z direction (or “trim” direction in the negative z direction). Move the clipping plane along the z axis. It seems that once the plane crosses z = 0 it starts to trim away more of the box wireframe then I would expect. The shaded box behaves exactly as expected.