title: Required input textbox is always invalidate on Angular 5 & KendoUI
body: <p>I try to make a form with KendoUI and Angular 4. I have some required field. All works fine except <code>&lt;input kendoTextBox required/&gt;</code> which is red even before the user write something in it.
  Here is the code:</p>
  
  <pre><code>&lt;form #identityForm="ngForm" class="k-form"&gt;
  
      &lt;label class="k-form-field"&gt;
          &lt;span&gt;Profession&lt;/span&gt;
          &lt;!-- This required input is red even before the user try to write something --&gt;
          &lt;input kendoTextBox required [(ngModel)]="profession" name="profession"/&gt;
      &lt;/label&gt;
  
      &lt;label class="k-form-field"&gt;
          &lt;span&gt;Country&lt;/span&gt;
          &lt;!-- This required input have the good behaviour --&gt;
          &lt;kendo-autocomplete required name="country" [(ngModel)]="country" [data]="countries"&gt;
          &lt;/kendo-autocomplete&gt;
      &lt;/label&gt;
  
  &lt;/form&gt;
  
  &lt;button [disabled]="!identityForm.valid"&gt;Submit&lt;/button&gt;
  </code></pre>
  
  <p>On <a href="https://www.telerik.com/kendo-angular-ui/components/inputs/textbox/" rel="nofollow noreferrer">KendoUI documentation</a>, it seems to works well.</p>
  
  <p>What should I need to modify to invalidate required field only when user click on submit button? Thanks</p>