Try also to check "normal combiner" in the "Game default option" tab. If it is checked, try with unchecking it. To me this seems to be the hottest trace.
Which render engine are you using? If it's DirectX you could try to change the "swap effect" method under the DirectX tab and see if this changes anything. If you are using OpenGL, you could try to use DirectX instead.
If none of these help I would propose to enable the "Display Tooltips" check box in the "General" tab. Than a tool tip will explain you every setting over which you are hovering your curser. That helps you determining if some of these settings might have an effect to your problem and change them.
Sorry for not being able to give you a precise instruction how to solve your problem but not being able to reproduce it, this is hard to do.
Let me know if one of these advices worked.