It is not possible to submit the artist edit form after adding and removing a URL whose type is not auto-detected.
Steps to reproduce:
1. Go to https://musicbrainz.org/artist/7e84f845-ac16-41fe-9ff8-df12eb32af55/edit
2. Change something (e.g., change the year of birth to 1002) so that there is a change to submit.
3. Paste http://www.example.org/ into the "Add another link" field. (Any URL whose type is not automatically detected should do.) Do not select a type for the URL.
4. Remove the newly added URL by clicking the symbol to the right of it.
5. Click on "Enter edit". The form is not submitted.