I mean that the screen switches to 640×480, but only the center 320×200 is used.Norbert wrote:(PS: I don't understand what you mean by 640x480, for me it's just 320x200 and fullscreen doesn't scale up.)
As the documentation says:
If a hardware resolution change is not possible (for whatever reason), the next higher resolution will be used and the display window centered on a black background.