As discussed on IRC: Changing one URL into another merges the two URLs, which (like any other merges) is almost impossible to undo.
I'm raising the priority, because of the License URL problem.
Agreed to fix within 3 months by http://chatlogs.musicbrainz.org/musicbrainz-devel/2012/2012-08/2012-08-20.html
In review at http://codereview.musicbrainz.org/r/2219/
I'm raising the priority, because of the License URL problem.