title: Angular 2 - [(ngModel)] not updating after [value] changes
body: <p>I'm setting the the value of an input calculating two other ngModels, and that seems to be working fine. But if I inspect my ngModel, it doesn't change at all. Let me show you:</p>
  
  <pre><code>&lt;ion-item&gt;
      &lt;ion-label&gt;Total price: {{product.totalPrice}}&lt;/ion-label&gt;
      &lt;ion-input 
          type="number"
          [value]="product.quantity * product.price"
          [(ngModel)]="product.totalPrice" 
          [ngModelOptions]="{ standalone: true }"&gt;&lt;/ion-input&gt;
  &lt;/ion-item&gt;
  </code></pre>
  
  <p>So here <code>{{product.totalPrice}}</code> shows the initial value, which is fine. If I change manually that input, the changes will be reflected on the expression, that is also fine. But that input will be <code>readonly</code> and it will be set by changing two other inputs. When I change them, I see the value on the input is updating just fine, but not the expression in the label. What's wrong there?</p>
  
  <p>It's really weird because the value in the input GETS UPDATED, but not the expression <code>{{product.totalPrice}}</code>, I guess the value is updating because the other fields are, but those value changes never actually hit the <code>ngModel</code> </p>
  
  <p>By the way, I'm using Ionic 2</p>