Amazon might have stated that it was automatic, but I have found that syncing on all of my Kindles (E Inks, KFire, apps) is not always automatic. Or more appropriately, it is not always quick to sync. With the E Inks and the KFire you should exit the book to the Home screen before putting the Kindle into sleep mode, otherwise it might not sync. I also make a habit of manually syncing just to make sure it does. I think that if left alone and with enough elapsed time they will sync automatically, but Kindle time is not always in tune with our time frame.