title: Angular 5 reactive form set mat-checkbox to check
body: <p>I am trying to use mat-checkbox with reactive forms on Angular 5.1.2 and Angular Material 5.0.2.</p>
  
  <p>Everything is working well except that when I use patchValue({amateur: [false]) it is still checked.  What is weird is I have other forms where I am doing the same thing and they work fine.  It also isn't just the amateur checkbox, it is all the checkboxes are checked.  Just using "amateur" as an example.</p>
  
  <p>The formControl amateur.value is always false.  However once the patched value is executed, the control is checked.</p>
  
  <p>What am I missing?</p>
  
  <p>HTML5</p>
  
  <pre><code> &lt;form [formGroup]="showClassGrp"&gt;
     &lt;mat-checkbox id="amateur" class="amateur" color="primary" 
        formControlName="amateur"&gt;Amateur&lt;/mat-checkbox&gt;
   &lt;/form&gt;
  </code></pre>
  
  <p>TypeScript</p>
  
  <p>FormBuilder works and display is correct.</p>
  
  <pre><code>this.showClassGrp = this.fb.group({
  
    ...
    amateur: [false],
    ...
  });
  </code></pre>
  
  <p>patch showClassGrp and all the checkboxes are checked even thou the formControl value for them are false.  </p>
  
  <pre><code>    this.showClassGrp.patchValue({
        className: [this.showClass.className],  //this works
        amateur: [false],  // this changed the display to checked.
        ...
  });
  </code></pre>