The situation you describe is not a bug. It is typical behavior due to the way OpenGL works. In the situation you describe with sheathing over studs, when you soom back beyond a certain point, the sheathing isn't thick enough to mask the studs. OpenGL considers the inside and outside faces to be in the same plane and in the same plane as the outside surface of the studs. You'll notice as you zoom in, the display changes and the studs no longer show. There are solutions to prevent the studs from showing through the sheathing. A common one and probably the easiest would be to put the framing groups or components on a layer separate from the sheathing. When you don't need to show the framing, turn that layer off.