Seems like you did you homework before posting. I don't have a answer for you question though. But my first thought was that since the Sony camera is 420TV it has longer sync pulses than the KX-1 with it's 520TV. I'm not sure about this since I only have two sony cameras so that's all I have tested.
The OSD uses a series of analog filters to filter out the sync signal. So it might be that the sync doesn't go low enough for the sync to work. Or it cannot sink enoght current to get the sync pulse to work each time.
But these are of course just guesses.
Could you upload a picture of a captured frame? Or a photo of how it looks?