title: animateWithDuration:delay:options:animations:completion: blocking UI when used with UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse
body: <p>I'm running a function to pulse a play icon:</p>
  
  <pre><code>- (void)pulsePlayIcon {
      if ([self isPlaying]) {
          return;
      }
  
      [[self videoView] playIcon].hidden = NO;
      [[self videoView] playIcon].alpha = 1.0;
  
      [UIView animateWithDuration:[self playIconPulseDuration] 
                            delay:[self playIconPulseTimeInterval] 
                          options:(UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse) 
                       animations:^{
                           [[self videoView] playIcon].alpha = 0.8;
                       } 
                       completion:^(BOOL completed) {}];
  }
  </code></pre>
  
  <p>This works wonderfully in iOS 5.0, but in 4.3 it blocks the UI. The UI doesn't respond. I read that this was the suggested way to do repeating animations in iOS version 4.0 or greater (>= 4.0). The culprit seems to be <code>UIViewAnimationOptionRepeat</code>. Do you see any obvious errors I'm making?</p>