If I copy an object, all surfaces appear when rendering the viewport. If I mirror the object and render the viewport, the front surfaces are not visible, while back surfaces are. If I rotate the view, surface visibility changes depending on whether the surface rotates to the back or front. All inner surfaces are always visible. This problem just cropped up in the last week. Using Version 5 SR6 64-bit from 9/18/2013.
Tangent Laser.3dm(1.6 MB)