Pressing the Back button won't let me exit the game (Android only)

We are aware of the problem, and it is on our list of things that need to be fixed. Until we can fix the problem, a workaround is to do the following:

1. Open either the in-game Store or the Options menu (the orange gear icon in the corner).
2. Close whichever window you opened in Step 1.
3. Press the Back button, which should now be working again. This should bring up the dialog box where you can confirm that you want to exit the game.