Oh, I actually hadn't implemented Android back button functions. I actually don't really own an Android so I wasn't familiar with that... Anyway, I now implemented them (well at least for now it goes back to the menu screen from the levels or notes screen). I might have it open up the menu dialog in puzzle or editor mode, if that's an appropriate function for the button.
Also, I think I fixed the crash (now checks if these certain variables were initialized).
Unfortunately now there's ads for cross-promotion.