After accidentally creating this relationship in the wrong direction, I expected that choosing "edit" and "change direction" would quickly fix it.
Instead I get "A relationship between Jag går på promenaden and Walking on Sunset already exists with these attributes."
http://ngs.musicbrainz.org/work/f6785f78-40cf-4893-b241-255c5fae1593/relationships
It now gives an internal error