I think what rogerzilla and fdigital meant to say is that you get a lot of the red edge phenomenon with the CV 21mm f4 on the M9 whether it is coded or not. This exhibits itself as a magenta cast up the left hand edge of the image (assuming its horizontal). The solution is to use Cornerfix software to remove it, but otherwise the 21mm CV is a nice lens.
The 21mm ZM Biogon f4.5 also produces a lot of red edge when mounted on the M9, but a coded 21mm ZM F2.8 is perfect.
Steve