I’ve seen this behaviour too after updating to iOS 5 and newer. I’ve also seen similar malfunctions on many other apps after updating iOS. Seems the apples;-) messed around with something in the iOS. To fix it you can try 2 approaches. Method 1: Switch off your iOS device by holding lock-screen button for some seconds (a switch-off slider will be displayed). Then restart your device. If this doesn’t help. Use method 2: Delete the app, then re-download/re-install the app. It might be necessary to apply “method 1″ once more.
Sorry for this inconvenience.