title: Tabbing does not work when adding a subview
body: <p>I have the following views:</p>
  
  <p><img src="https://i.stack.imgur.com/Yfoj6.png" alt="xib"></p>
  
  <p>The xib contains a 'mainview' and a 'page1view' outlet (both NSViews).</p>
  
  <p>I have the following code:</p>
  
  <pre><code>- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
  {
      [mainView addSubview: page1View];
  }
  </code></pre>
  
  <p>Which when I run, it looks like this (as expected):</p>
  
  <p><img src="https://i.stack.imgur.com/IzTti.png" alt="Output"></p>
  
  <p>The only problem is that tabbing between elements no longer works (With placeholder1.1 selected, if it hit tab, nothing happens).</p>
  
  <p>Is this a bug in OSX, or am I doing something wrong here? If it is a bug, does anyone know a workaround?</p>