1. https://musicbrainz.org/artist/244f9821-c21b-4c82-abfc-c9c82199ec19/edit
2. click the first empty URL input field
3. type V
4. type BACKSPACE
5. type V

The last step can't be performed as the focus was lost after typing BACKSPACE.
It is not because of some BACKSPACE protection (to avoid navigate out of page) because the following does the same problem

1. https://musicbrainz.org/artist/244f9821-c21b-4c82-abfc-c9c82199ec19/edit
2. click the first empty URL input field
3. type V
4. type HOME
5. type DELETE
6. type V

Behaviour : ○ works (no bug, you can type the last V) / × doesn't work (bug, focus is lost)