It says who unfriended you since you installed the app, not before that. It will save a list with all your friends and the next time you open the app it will check if someone deleted you. We can't read mind and check who deleted you before the installation of the app. Be reasonable! Simply log in and press "refresh friends list". Wait for your friends list to be imported and you are all set up. Whenever you want to check if someone deleted you, open the app and hit the refresh button again. You will see how many friends you added or lost since last time you checked. Press the "all friends" button and see the list with your friends, or press the "history of changes" button and check the list of all the friends you added or lost since you installed the app.