I was contemplating whether to submit this as a suggestion or a bug but since there's a workaround I'm going with 'Suggestion'.
- Create a new RSS feed importer with a valid URL
- Save the importer
- The URL becomes invalid
- Edit the RSS feed
- Mark the RSS feed as inactive
- Save it
- Error message displayed that the URL is invalid
- Unable to save the feed to mark it as inactive
- When in 'edit' mode, do not validate the URL when saving the feed if it is flagged as inactive.
- Do not edit the feed - Instead, when listing the RSS feeds, change the active flag from there instead of clicking on it to go into 'edit' mode. The feed is not validated when flipping the active flag from the feed listing so it can be updated.