After some difficulties, I realise that I am offered the USB capture options I expected, in certain circumstances.
Now when I save them and restart the system, these settings are ignored. Everything comes back to 'automatic' and I am no longer offered these options.
How come?
The circumstances I am refering to are setting the device to custom > /dev/video14 then saving, then restarting, then again here are the right options offered. Useless.