title: Flip Animation not working
body: <p>I have a Custom view. This custom view has two UIImageViews - imageview1 and imageview2.</p>
  
  <p>[UIView beginAnimations:nil context:nil];
      [UIView setAnimationDuration:2.00];
      [UIView setAnimationDelegate:self];
      [UIView setAnimationDidStopSelector:@selector(transitionDidStop:finished:context:)];
      [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft forView:self cache:YES];
      if(frontVisible) {
          [imageview1 removeFromSuperview];
          [self addSubview: imageview2];
      }
      else {
          [imageview2 removeFromSuperview];
          [self addSubview: imageview1];
      }
      frontVisible = !frontVisible;
      [UIView commitAnimations];</p>
  
  <hr>
  
  <p>The image changes from imageview1 to imageview2 and viceversa but I dont get the flip effect. Instead I see the fading out of one image as the other appears.</p>