I couldn't reproduce this on a sandbox, but I can reproduce it on the live servers, so I'm not sure what's going on there...
Steps to reproduce:
- Edit a URL, leave the edit open
- Enter a remove relationship edit to remove the relationship using the URL
- Accept the remove relationship edit
- Accept the edit URL edit
Expected result: There are no relationships left, so the URL gets deleted.
Actual result: The URL is still in the database despite being unused.
An example of where this happened is https://beta.musicbrainz.org/url/142f899a-0749-468b-b569-7cccca48802c