title: angular Material Tabs do not change their content
body: <p>I'm starting to learn AngularJS and Angular Material. </p>
  
  <p>I have a problem on understanding the md-tabs.</p>
  
  <pre><code>&lt;section layout="row"&gt;
      &lt;div layout="column"&gt;&lt;img id="ApplicationLogo" src="https://material.angularjs.org/latest/img/icons/angular-logo.svg"&gt;&lt;/div&gt;
      &lt;div layout="column" id="ApplicationTitle" layout-align="center start"&gt;Application Title&lt;/div&gt;
      &lt;div layout="column" id="ApplicationWelcome" flex layout-align="center end"&gt;Angemeldet als Test User&lt;/div&gt;
      &lt;div layout="column" layout-align="center center"&gt;&lt;img id="ApplicationAvatar" src="http://findicons.com/files/icons/1072/face_avatars/300/d05.png"&gt;&lt;/div&gt;
  &lt;/section&gt;
  </code></pre>
  
  <p>Here is a demo: <a href="http://plnkr.co/edit/72ZNb70BjSM6xP7RnSvH?p=preview" rel="nofollow">http://plnkr.co/edit/72ZNb70BjSM6xP7RnSvH?p=preview</a>   </p>
  
  <p>Any hint why my tabs do not change their content?</p>