When you have multiple Yamaha Musiccast devices, and you are in the view of one device, and you press the power button on top right, it will wrongly affect a different device. You can see that when you go back to the overview of all devices. It seems like the power button is always affecting the first in the list of all devices instead of the current device.
I’m not currently seeing this issue with my RX-A760. When I turn Zone 2 off, it only changes that zone. The main power state stays the same. I’m not sure what would be causing the issue for you.
Please notice that it works for me well in the main screen where you see all zones. But it does not work, when you enter a zone (e.g. when NetRadio plays and you see the Volume bar on bottom and Audi-Selections on the left). When you then use the power-button on the top right (see attached screenshot), only then it switches the wrong zone on/off for me.
Do the other commands on that screen work, like volume control?
Do you have an Android or iOS device you can also test? Does this problem exist in the Home Remote app on those devices as well?
Can you go to the Settings page & create a backup then send that to me? Just send it to firstname.lastname@example.org or private message me on here. Remove any other devices you don’t want me to see. Yamaha is controlled using private/local IP addresses, so there won’t be any sensitive information in a backup containing only those devices.