The update for Adding Machine HD is in the App Store now. It fixes a bug that came with iOS 5. In testing, sometimes upgrading the app alone is enough to fix the bug. In other instances you will need to delete the app and then reinstall. To delete the app you hold the icon for several seconds. All your icons will begin to wiggle and a black “X” will appear. Tap the icon you want to delete. After reinstalling tap a button to upgrade, Apple keeps records of what you have purchased and should not charge you.
Sorry for the inconvenance and sorry it took so long to fix, it was a real mystery for a long time.