An unticked checkbox is absent from a form submission entirely, so
"rotate unticked" and "rotate never mentioned" arrived at the parser
looking identical - and rotate defaults to on, so it snapped straight
back every time. Add a hidden marker the options form always sends, so
absent-but-submitted can be read as unticked.
Same bug silently reset the field list when every field was unticked;
that is fixed by the same marker. rotate_default lets a saved site-wide
preference apply on a fresh arrival without overriding an explicit
untick on the page.
jessikitty