I'm not sure what the expected behaviour is with updating books having upgraded the app to 1.5 but here's what happened for me:
On initially loading 1.5 the home screen had an offline resources section with 59 book updates available (I suspect this was every book I had downloaded); pressing this brought up a dialog to update books, but there were no book titles/icons, just lots of rows with 'no cover' image place holders. I closed that dialog without doing anything, and the book update section disappeared from the home screen. Tried rebooting the app and all downloaded books are gone.
What was supposed to happen? 
