title: UIView animateWithDuration: does not animate in iOS 7
body: <p>In Xcode project, I have animated by using <code>UIView animateWithDuration:</code> works in iOS 6. In iOS 7, on initially launch the animation works fine. But when I enter into background and again enter into app (foreground), <code>UIView animateWithDuration:</code> does not work. </p>
  
  <p>Any idea why this is happening?</p>