Just now was I listening to "Devil Without a Cause" by Kid Rock, off the title off the same name when I realized that my uploaded music to the Google Play Music cloud is not the same files that I uploaded, because the song was **edited**! I had the exact thing happen on Spotify a long time ago.  Putting further proof to my idea that suggests your "uploaded music" isn't really yours at all, but rather a "key" to that unlocks it from their copy they already have.  I doubt they have million copies of the same song stored, rather they have a single one.  The first to upload something acts as a "standard" until something that meets higher specs is met.  This has got to be how it is.