title: UIScrollView zoomToRect scrolls the view when It should not
body: <p>I made a simple test project to show the problem:
  there is an imageview which is contained in scrollview 
  view -> scrollview -> imageview </p>
  
  <p>scrollview's content size is same as imageview size = (AllWidth, AllHeight). </p>
  
  <p>The problem is that if scrollview is scaled EXACTLY to fit image by width (<code>scrollView.zoomScale = 320.0/AllWidth;</code>) then calling zoomToRect</p>
  
  <pre><code>[scrollView zoomToRect:CGRectMake(0.0,  0.0, AllWidth, AllHeight) animated: NO];
  </code></pre>
  
  <p>does scroll imageview to the bottom for some reason. But nothing is expected to happen with UI</p>
  
  <p>if scrollview is NOT scaled EXACTLY to fit image by width (<code>scrollView.zoomScale = (320.0-1)/AllWidth;</code>), then calling zoomToRect does what is expected - image is scaled and not scrolled to the bottom.</p>
  
  <p>i noticed that in 'buggy' case ContentOffset.y is changed, but i have no any idea why.</p>
  
  <p>to reproduce the issue, start new project, in viewcontroller.h file add <code>&lt;UIScrollViewDelegate&gt;</code>; viewcontroller.m is here: <a href="http://pastebin.com/bPUtuYn1" rel="nofollow">http://pastebin.com/bPUtuYn1</a> (in test project you will need double tap green image, then change "320.0-1" to "320.0" and try again)</p>