In game music plays over itself.

The game will occasionally start playing a track of music even if there is a track already playing. I.e. if calm1 is playing it might start playing calm2. Once the track that started first is over the other tracks that started while the first track was being played also stop. This also happens with juke boxes; when you take out the music disc, the song that is playing will not always stop, and you can hear multiple tracks being played over each other that way as well.