The only thing connected to the TV is an Anthem MRX 540 surround receiver.
When I change the source on the TV, so that it displays the video signal from the receiver, the TV seems to send an HDMI CEC command to the receiver, telling it to change input to something that doesn't make sense.
So changing back and forth between TV source and the receiver source, triggers an input change on the receiver.
It doesn't always change to the same input on the receiver. It depends what input I was on before I switched from TV to receiver on the TV.