title: Popover with embedded navigation controller doesn't respect size on back nav
body: <p>I have a UIPopoverController hosting a UINavigationController, which contains a small hierarchy of view controllers.</p>
  
  <p>I followed the docs and for each view controller, I set the view's popover-context size like so:</p>
  
  <pre><code>[self setContentSizeForViewInPopover:CGSizeMake(320, 500)];
  </code></pre>
  
  <p>(size different for each controller)</p>
  
  <p>This works as expected as I navigate forward in the hierarchy-- the popover automatically animates size changes to correspond to the pushed controller. </p>
  
  <p>However, when I navigate "Back" through the view stack via the navigation bar's Back button, the popover doesn't change size-- it remains as large as the deepest view reached. This seems broken to me; I'd expect the popover to respect the sizes that are set up as it pops through the view stack.</p>
  
  <p>Am I missing something?</p>
  
  <p>Thanks.</p>