Passing multiple ID's in a query doesn't return all data

Hey guys, we are running into the exact same issue now. Here are some example requests:

http://developer.echonest.com/api/v4/song/profile?api_key=APIKEY&bucket=audio_summary&bucket=id%3Aspotify&bucket=tracks&format=json&track_id=spotify%3Atrack%3A0e7MKWjKXnaXbBfZskfSG6&track_id=spotify%3Atrack%3A7wDTZRmHTSbAdk1VTHjC4t

This request contains two spotify URIs but only returns one song: Run to the Hills by Iron Maiden.

If we perform the same API request but with just one track ID: http://developer.echonest.com/api/v4/song/profile?api_key=APIKEY&bucket=audio_summary&bucket=id%3Aspotify&bucket=tracks&format=json&track_id=spotify%3Atrack%3A7wDTZRmHTSbAdk1VTHjC4t

the other song is returned: Run to the Hills by Erik Grönwall.

Any ideas?