I changed my mind about “Most important: in the hook for validating updates, set-screen-option, pass the $value back if your plugin does not recognize the $option ! It’s probably for another plugin!”
It’s better to go with what the hook suggest and send back $status (which is false) if you don’t know the $option.
To prevent conflicts with other plugins, instead I put in a $_GET[‘page’] check before adding the validator filter.