title: Polymer: Imperatively set property doesn't changes
body: <p>I'm stuck for like two days now and I'm shooting blanks at this problem I'm about to describe.  </p>
  
  <p>I made a plunker: <a href="http://plnkr.co/edit/OrUiqcFfb70VFtO06sNT" rel="nofollow">http://plnkr.co/edit/OrUiqcFfb70VFtO06sNT</a></p>
  
  <p>So, I have <code>&lt;main-element&gt;</code> - this element contains two children: <code>&lt;child-element&gt;</code> and <code>&lt;sub-main&gt;</code>. Both of these elements binds on <code>owner</code> object that is set in <code>&lt;main-element&gt;</code>. Like this:  </p>
  
  <p><code>&lt;child-element owner="{{owner}}"&gt;&lt;/child-element&gt;</code>  </p>
  
  <p>Now, <code>&lt;sub-main&gt;</code> contains another element - <code>&lt;sub-child-element&gt;</code>. </p>
  
  <pre><code>&lt;template&gt;
      &lt;sub-child-element id="sub"&gt;&lt;/sub-child-element&gt;
  &lt;/template&gt;
  </code></pre>
  
  <p>But it binds <code>owner</code> property imperatively:  </p>
  
  <pre><code>attached: function() {
      this.$.sub.owner = this.owner;
  }
  </code></pre>
  
  <p>As you might have guessed <code>&lt;sub-child-elements&gt;</code> doesn't see changes made to <code>owner</code> object. I have tried to sprinkle <code>this.set</code> and <code>this.notifyPath</code> all over the place but it did not helped. </p>
  
  <p>Any way to make this work? Is it even possible do do what I want?</p>