Hello All,
As @andybob mentioned, the Radio on/off settings are saved as zone specific settings. Turning it off for your desired zone should keep it saved as off for that specific zone.
Just a note, if you group the “Radio Off” zone with a “Radio On” zone, the two zones will merge to have the Radio value of the first zone and will retain this value even after they are ungrouped unless manually configured as otherwise when ungrouped.
If you are seeing different behavior and the Radio function for one of your zones turning on after you have turned it off please let me know, otherwise this is expected behavior here.
As for defaulting the Radio function to off globally, please take a look at the feature request thread @andybob linked above.
Thanks,
Noris