CN204 isn't shown on the circuit section I posted, but Q211 is just a switch, with the input on the emitter, and the output on the collector. As R274 is powered from this switched 9V rail, then the Q212 regulator is switched as well.
You already know that you can't have the different voltages on the same piece of track - is one perhaps on mains, and the other on battery?.
You already know that you can't have the different voltages on the same piece of track - is one perhaps on mains, and the other on battery?.