response=sorts not working?

I'm trying to use the API and for the most part, I enjoy it very much. However, I'm trying to retrieve the releases for an artist sorted by releaseDate.

According to the documentation, I should be able to add response=sorts to retrieve the available parameters to sort by. However, adding response=sorts gives me a 400 error (Bad Request). I am able to sort by artistName (sort=ArtistName+), the example from the documentation, but something like sort=releaseDate+ (just a guess) doesn't work.

Works:
http://us.music.yahooapis.com/release/v1/l...32849028?appid=[my_appid]
http://us.music.yahooapis.com/release/v1/l...istName+&appid=[my_appid]

Doesn't work:
http://us.music.yahooapis.com/release/v1/l...se=sorts&appid=[my_appid]
http://us.music.yahooapis.com/release/v1/l...aseDate+&appid=[my_appid] (just a guess)