Just signed up for Premium not even half an hour ago. Everything - downloading songs, picking songs I want to hear in any order, etc - works fine, but the app isn't letting me go back to previous songs. The back icon is grey and doesn't work. I've signed out, restarted the app, and even restarted my phone and still, nothing. After paying ten bucks, I'd like to have all of the features promised. Any tips or suggestions?