title: UISlider missing track images in iOS 5
body: <p>I have a UISlider, and I set custom trackImages and thumbImage, using the following code:</p>
  
  <pre><code>[progress setMinimumTrackImage:[UIImage imageNamed:@"scrubbar-inactive.png"] forState:UIControlStateNormal];
  [progress setMaximumTrackImage:[UIImage imageNamed:@"scrubbar-active.png"] forState:UIControlStateNormal];
  [progress setThumbImage:[UIImage imageNamed:@"scrubbar-ball.png"] forState:UIControlStateNormal];
  [progress setThumbImage:[UIImage imageNamed:@"scrubbar-ball.png"] forState:UIControlStateHighlighted];
  </code></pre>
  
  <p>Everything works fine, but in iOS 5 infrequently I get only the thumbImage and no trackImages underneath.</p>