I don't know if it's relevant, but the change data for that shows:

{"entity":{"name":"http://en.wikipedia.org/wiki/Born_and_Raised_(Cormega_album)","id":733573},"new":{"description":null},"old":{"description":""}}

So it looks like the description got changed null -> "" in any case. Do you remember what the original vs. changed URL was for that edit?

nikki's reproduced this with http://beta.musicbrainz.org/edit/18890163 – evidently there was no actual change to the URL, it's just the description changing from "" to null... whatever that means.

I think the fix for this may simply be:

UPDATE url SET description = NULL WHERE description = '';

or so.

Except not all at once, of course, given there's currently ~800k URLs with a description that's the empty string (and about 540k with it set to null).

Setting this to the schema change, since we've decided that's the appropriate time to run huge changes like this.

Dropping URL descriptions entirely would fix this nicely

This will be fixed by MBS-3791