title: ngx-bootstrap accordion isOpen and isOpenChange causing hang
body: <p>I am probably doing something stupid here.
  I have an accordion with multiple groups. When one is open the others should close and when an action has been performed on one, then the next one opens. You can obviously go back (like a stepper).</p>
  
  <p>The basic format is this:</p>
  
  <pre><code>&lt;accordion closeOthers="1"&gt;
      &lt;accordion-group (isOpenChange)="state.categoriesOpen = !state.categoriesOpen"
          [isDisabled]="!categories?.length"
          [isOpen]="state.categoriesOpen"&gt;
          &lt;div class="btn btn-link"
              accordion-heading&gt;
              &lt;span&gt;1.
                  &lt;span *ngIf="!chosenCategory || !criteria"&gt; Choose category&lt;/span&gt;
                  &lt;span *ngIf="chosenCategory &amp;&amp; criteria"&gt; Category | &lt;b&gt;{{chosenCategory?.name}}&lt;/b&gt;&lt;/span&gt;
              &lt;/span&gt;
              &lt;mat-icon&gt;{{ state.categoriesOpen ? 'expand_less' : 'expand_more' }}&lt;/mat-icon&gt;
          &lt;/div&gt;
  
          &lt;!-- some content here --&gt;
      &lt;/accordion-group&gt;
  &lt;/accordion&gt;
  </code></pre>
  
  <p>In my code I have this state object defined:</p>
  
  <pre><code>state: any = {
      categoriesOpen: true,
      criteriaOpen: false,
      attributesOpen: false,
      formulasOpen: false,
  };
  </code></pre>
  
  <p>By default the first group is open. But for some reason it just hangs here forever.
  When I remove the <strong>[isOpen]</strong> it works.</p>
  
  <p>Does anyone know why this is broken?</p>