title: Angular 2 - material 2 checkbox - checkbox [checked] by default
body: <p>I'm using <code>md-checkbox</code> in a <code>FormArray</code>. </p>
  
  <pre><code>private protocolArray: FormArray = new FormArray([
      new FormControl('tcp'),
      new FormControl('udp')
  ]);
  
  &lt;div class="form-group" formArrayName="protocol"&gt;
        &lt;md-checkbox formControlName="0" [checked]="true"&gt;TCP&lt;/md-checkbox&gt;
        &lt;md-checkbox formControlName="1" [checked]="false"&gt;UDP&lt;/md-checkbox&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>When it renders both are checked by default. If I get rid of the <code>md-checkbox</code> and make it a normal <code>input type="checkbox"</code> things render perfectly. </p>
  
  <p>What gives?</p>