In the new URL editor the available type options of the select menu are filtered based on the entered URL to show only the applicable options and their headings. I noticed that the "Discogs" link type is shown under the "get the music" heading instead of the "other databases" heading where it belongs:

I guess this happens because "get the music" is the last disabled option heading above "Discogs" while "other databases" is not a disabled option. It seems like you have to trigger an error (e.g. enter a duplicate) to make this select menu appear at all, otherwise Discogs just gets auto-selected and you won't notice the issue.