Okay, maybe not quite a bug but more a "feature". If you mute the music in the launcher, you can't turn it on in-game. You have to quit and load it up again. I tried putting the slider up, but closing the menu in-game just resets it to '0' again. Edit: Also, unchecking 'Mute' in the launcher resets the music volume to full, not to the last chosen setting.