Basically true but given I've managed on occasion to get the first click and then get another twenty litres into the tanks, it's not the whole story. Depends a lot on the sensitivity of the pump cut off and the rate of flow; a fast pump seems to flow a lot faster than the balance pipe between the two tanks can handle, so a false "full" can happen long before the left hand side tank is anywhere near full. Over filling can certainly cause nasty misfires and warning lights as the vapour breather system for the tanks gets filled with liquid petrol.
I have of course also had a pretty much instant overflow on filling past the first click!
