Ah. Feature of unRaid itself. Any update to the container will also bring in any missing ports / variables etc under the assumption that the update brings new features that might require that.
I'd recommend that the container is set up to ignore variables that aren't actually filled out.
Alternatively, you can disable that feature completely by editing the template within /config/plugins/dockerMan/templates-user and removing the <TemplateURL> entry. (Although at that point FCP will complain, but that can be ignored)
Over the years, the updating of the template has proved to be useful as the apps themselves evolve, (ie: webUI entry changes), but it's never going to be a perfect system.
Because of the maintainers who did fill out that entry in the first place did it wrong (fully 50% of them), CA's appfeed now handles it and there is no more access to that entry in the webUI anymore.