What's your display configuration? Seems it's asymmetric ... currently the center is taken from the center of the virtual area, as people with two symmetric displays would want it in the center. But if you are using the secondary screen as a side window, that would require an asymmetrical frustum setup. Hmm, something similar is being done for the stereoscopic rendering, where the projection center can be offset, but currently it's not possible to configure it for the normal mode.