Allow urlencoded string in URI

[eluser]erik.brannstrom[/eluser]
For example /music/artist/Sigur+Rós, which to me looks entirely legit, returns the "The URI you submitted has disallowed characters" message. It works just fine using Sigur+Ros, and % should be an allowed charachter, so the only thing I can think of is that somewhere along the road, the ó gets decoded to ó.