title: Angular mat-button-toggle rendering does not bind to ngModel
body: <p>I have been trying to fix a bug where the <code>mat-button-toggle</code> element renders as "selected", even though the <code>ngModel</code> has a <code>false</code> value. And I found something, that at least to me looks strange. Consider a code example:</p>
  
  <p><code>.html</code></p>
  
  <pre><code>&lt;mat-button-toggle 
      [(ngModel)]="myVar" 
      (change)="toggle()"
      ngDefaultControl
      name="myVar"&gt;
    TOGGLE ME
  &lt;/mat-button-toggle&gt;
  </code></pre>
  
  <p><code>.ts</code></p>
  
  <pre><code>myVar = false
  toggle() {
      // do nothing!
  }
  </code></pre>
  
  <p><strong>I expected:</strong></p>
  
  <p>After you click on the button, it does NOT render as "selected" because <code>myVar</code> still has <code>false</code> value.</p>
  
  <p><strong>What actually happens:</strong></p>
  
  <p>The button renders as "selected" disregarding the actual <code>myVar</code> value.</p>
  
  <p>I have a feeling I miss some core Angular understanding here that makes me unable to understand why doesn't it work like I expect it to. Can you help me understand what is wrong here?</p>