If you are a Google Music subscriber and a Windows user then you will want to check Outcoldplayer a 3rd party Google Play Music app for Windows 8.1. The app supports offline playback and all-access subscriptions so you all of the Google Music features on Windows 8.1. The app has just been updated and it fixes loading issues with Google Music library song duplicates.
##08/14/2014 – Version 3.1.8
* Fix issue with loading Google Music library with song duplicates