That is.. well.. curious
As far as I've seen this upgrade done, you just remove the 4:3 and throw in the 16:9 and you are done. The only times I got the scrolling image were when mixing PAL and NTSC formats (ie: PAL camera on the reverse camera input which is NTSC, just an example).
Try the following scenario:
-ignition off
-unhook the MK4 (or whatever) unit, the blue and maroon connectors
-at this point with ignition on and your 4:3, you should see the ugly blue style menus
-ignition off
-swap the 4:3 with the 16:9
This is just a shot in the dark, based on the assumption that you are mixing US and EU parts.