title: Angular (change) event not firing on all changes
body: <p>I have an Angular 7 app that contains a text input. The value of the text input is bound to a component level variable <code>accountNumber</code>.</p>
  
  <pre><code>&lt;input type="text" [(ngModel)]="accountNumber" (change)="isAccountNumberFlagged(accountNumber)" /&gt;
  </code></pre>
  
  <p>I have a component method <code>isAccountNumberFlagged(number: string)</code> that checks to see if the <code>accountNumber</code> is flagged and if it is display a warning (by making a specific  element visible. I have this method bound to the <code>change event</code> and it works as expected.</p>
  
  <p>What doesn't work as expected is when I change the value in the text input after having entered a value that has been "flagged" and tab to another control. The <code>(change)</code> event does not fire in these cases. </p>
  
  <p><strong>Sequence of events</strong></p>
  
  <ol>
  <li>Component loads</li>
  <li>Change the value in the text input = <code>(change)</code> event fires</li>
  <li>Enter a flagged account number = <code>(change)</code> event fires and flagged warning displays</li>
  <li>Change the value in the text input = <code>(change)</code> DOES NOT fire (even if I enter another or the same flagged account number)</li>
  </ol>
  
  <p>Clearly I am missing something about how the <code>(change)</code> event works. What am I doing wrong?</p>