What I'm trying to do is slightly odd. I have some patches that I'm rendering with OpenGL evaluators. It's convenient to specify one half of the geometry and draw the other half after calling glScale to mirror about an axis. I'd also been using GL_AUTO_NORMAL. I expected glScale to flip the normals on the inverted half, but for one sided lighting this seems to work fine. When two sided lighting is enabled however the inverted half of the geometry is not lit at all. Now I can just make sure that all my stupid patches are pointing the right way, unfortunately however I'm not the only one working on the project and I'm not sure if two sided lighting won't be needed for other reasons. So I wondered why this was, and whether there was any workaround. (Th most obvious one is just to invert the geometry manually when building up the display list I suppose.)