You need to place your music in the sound folder, not the music folder
the new map pack also had that problem, they updated their topic that you had to place the new music in the sound foleder in stead of the music folder.
same now goes if you add your own music to your map (I just tried that and everything worked)
but your musci must be in your sound folder. also the name you give in the map maker must be exact the same as your music file. one wrong single letter makes that the music doesn't work.