When you Play a Music disk and leave the world while it is playing and then go back into the world the Music restart and Plays for ever until you quit the game or reload resource pack (F3+T). Even if you pause the game or leave the world the Music disk continues playing.

Steps to reproduce:
1. Place down a Jukebox.
2. Play a music disk.
3. Leave the world.
4. Leave the world and go back into it.

You will see that it keeps playing, even if you pause the game or leave the world. The only ways to stop the music disk are quiting the game or reloading the resource pack (F3 + T). please try to fix it for the next snapshot, thanks .