I found a very strange thing today in Minecraft, or it could just be my Bukkit server. When I was trying to get music discs ("stal" in particular) and got 11 instead. Is this a new feature or a Bukkit plugin (I have all of the Essentials plugins and PlayerHeads)?
Music disk 11 is just another possible music disk.
From the Minecraft wiki:
"The recording seems to be of a person running across (or maybe breaking) different block types and later on, stopping to use equipment of some kind, cough, and then continue running with a hastened pace. The block sounds similar to that of dirt and stone. The person struggling, and haunting background noises are heard throughout the recording. Strange noises of barking or wind blowing are heard near the end before abruptly stopping. One can hear static noise akin to what would be expected of a broken record after this point before ending. Up until 1.4.3, it was impossible to get this disc in Survival. Now it is dropped by Creepers in the normal manner."
This disk is not from your bukkit server and is not a glitch. It's just an odd thing they threw in there to keep the game interesting. Like rotting flesh. Most won't have a use for that...