I don't think that's coming from the nav sofware version, as it's not related to the nav system, tv tuner is the module driving the reverse camera, morever you are able to get a fine picture through the AV input.
You can try to upgrade the nav soft version though ,it's better to have the latest version...
do you have an other external source plugged into the AV pinouts ? (dvd?)
if yes, did you try to remove it ?
do you have a multimeter to pick up the voltage of pin17 to be ensured it's right 0V when reverse shift is engaged?