When placing a music disc into a Jukebox while background music is playing, usually the background music would stop and allow the music disc to play in its place, although this i not the case in 14w11b. In 14w11b the Background music will continue to play as the Jukebox plays the song. This bug has been tested with all music discs, Although I am not sure if this i just an Isolated incident within my own PC, As it may just be the Minecraft that is installed on my computer, although i severely doubt this.