In some graphics cards, whatever screen resolution you set your graphics card to output, the C2 unit always shows it as another resolution, such as 1920x1200 60Hz Rb.
This is not because the C2 unit has incorrectly detected it - it means that your graphics card is scaling your intended resolution to the highest resolution that the C2 unit supports.
I.e. the graphics card is actually outputting 1920x1200 60Hz Rb. (The 'Rb' means reduced blanking.)
This can usually be turned off in the graphics card driver.