title: Angular2 doesn't detect changes in Array
body: <p>I am on an Ionic2 / Angular2 project. There I have a </p>
  
  <p><code>*ngFor="let item of items | async | customPipe"</code> </p>
  
  <p>in my code. The <strong>async</strong> is because <code>items</code> is an <strong><code>Observable&lt;Item[]&gt;</code></strong>. My <code>customPipe</code> is working fine on the first run. But when I make any change to one if the items that would filter it out through my <code>customPipe</code> it is still shown.</p>
  
  <p>What's the problem? Is the <code>*ngFor</code> only run once? Or do I have to force a DOM-update? Thanks for any help.</p>