Multiple artist tags not indexing?

I have a Raspberry Pi 2 with OpenElec (Kodi v14.2).
I have my music library tagged and everything is working except one thing. When I have multiple artists (on a track) the track/album isn’t indexed in the library. (A track with multiple artists) I can still play it by choosing to play files and while playing the album/tracks it displays the artists correctly as well as title and album. So, everything is displaying correctly when playing but Kodi will not index the tracks/albums with multiple artists collaborating. (xxx feat. yyy)
Compilations seem to work as long as each track only has one artist. (Problem = one track with multiple artists.)
I use Mp3tag for tagging and \\ as separator which creates a artist field for each collaborating artist on the track. (xxx\\yyy = 2 separate artist fields)
I installed Musicbrainz Picard to double check that everything was correct and it confirms that all is ok.

I have no idea what to do? Everything is done correctly from what i can tell and yet, it will not add the tracks/albums to the library. What do do?
Please help me.