I found this bug while playing on peaceful in survival mode. A new song (probably added in 1.7.2) started playing. After a while, when that song was still going, another song started playing, and they were playing at the same time. Needless to say, it was pretty annoying, and i had to turn down the music volume. It happened 5 days ago, and i couldnt recreate it, yet. It may only be a minor bug, but it can be really annoying.