Here's an example -- from the homescreen, click a Music widget. The Music app opens and shows the song I was listening to. I want to go back to the playlist I was playing from so I hit back. Instead, I'm dumped back to my home screen. you have to hit the Google Music icon in the top-left to go back within the Music app. I don't mind having to hit back a couple of times because I've learned that you can just keep hitting back and you'll eventually get where you were.