This sounds like your camera... I have had my "cheaper" cameras mess with me on things such as this where video would just stop, lose grid, etc.. and then all of a sudden things would come back for no apparent reason, and the only common denominator that I could find was they got wet from a car wash.. even though they were supposed to be water tight.
See if your camera has any jumper wires on it... a few of mine did and after uninstalling them, checking the jumper settings (remove/reintstall jumper), and reinstall the camera and the features would return....
Just a thought... otherwise you might have to get a new camera.
*bump*
Is it a setting or should I pickup a new reverse camera ?