title: <textarea> default content disappears when adding formControlName the <textarea> element
body: <p>I'm trying to create a Reactive Form in Angular 4.0.2, which has a <code>&lt;textarea&gt;</code> field with default content, pulled from the database. The content in the <code>&lt;textarea&gt;</code> is showing without any issues, but when I add the <code>formControlName="sectionContent"</code> to the <code>&lt;textarea&gt;</code> element, the content from it disappears.</p>
  
  <p><code>&lt;textarea formControlName="sectionContent "&gt;{{ section.sectionContent }}&lt;/textarea</code>></p>
  
  <p>This issue is only happening with the <code>&lt;textarea&gt;</code> element, as I have other <code>&lt;input&gt;</code> fields in the form, but those contents are still appearing.</p>
  
  <p>The FormGroup looks like this:</p>
  
  <pre><code>this.sectionForm = new FormGroup({
    sectionTitle: new FormControl(),
    sectionContent : new FormControl()
  });
  </code></pre>
  
  <p>Did anyone encountered this issue?</p>