1) go to url like http://musicbrainz.org/edit/relationship/create_url?entity=9cb1e53d-3706-40ed-99d3-2ec881a19202&type=release

2) paste a url with a leading space, like " http://www.discogs.com/Sideshow-Philly-Soundworks-EP/release/852749"

3) notice that the javascript doesn't remove it, and therefore doesn't detect it's a discogs url.

4) get slightly annoyed at having to be more careful while pasting urls