title: UIButton and UIControlEventState issue
body: <p>I'm having a very specific "bug" in my iPhone application. I'm setting two images for the highlighted and normal states of a button. It works as expected when you "press" and then "touch up" at a slow pace, but if you click/tap it quickly, there's a noticeable flicker between states. Is this a known bug or am I setting the states incorrectly?</p>
  
  <p>Here's the code that creates the buttons:</p>
  
  <pre><code>UIImage *normalImage = [[UIImage imageNamed:@"btn-small.png"] stretchableImageWithLeftCapWidth:10.0f topCapHeight:0.0f];
  UIImage *highlightedImage = [[UIImage imageNamed:@"btn-small-down.png"] stretchableImageWithLeftCapWidth:10.0f topCapHeight:0.0f];
  
  [self setBackgroundColor:[UIColor clearColor]];
  
  [self setBackgroundImage:normalImage forState:UIControlStateNormal];
  [self setBackgroundImage:highlightedImage forState:UIControlStateDisabled];
  [self setBackgroundImage:highlightedImage forState:UIControlStateHighlighted];
  
  [self setAdjustsImageWhenDisabled:FALSE];
  [self setAdjustsImageWhenHighlighted:FALSE];
  </code></pre>
  
  <p>When a button is tapped it simply disables itself and enables the other button:</p>
  
  <pre><code>- (IBAction)aboutButtonTouched:(id)sender
  {
      aboutButton.enabled = FALSE;
      rulesButton.enabled = TRUE;
  }
  
  - (IBAction)rulesButtonTouched:(id)sender
  {
      rulesButton.enabled = FALSE;
      aboutButton.enabled = TRUE;
  }
  </code></pre>
  
  <p>Any thoughts on this quick-click flicker?</p>