title: mat-select disabled is not picking up on the variable from the scope in angular5
body: <pre><code>&lt;div class="bulk-actions-container"&gt;
    {{ selectedInstances.length }}
      &lt;mat-select placeholder="{{'common.bulk.actions.title'| translate }}" disabled="selectedInstances.length === 0"&gt;
          &lt;mat-option [value]="'dueDate'"&gt;Change Due Date&lt;/mat-option&gt;
      &lt;/mat-select&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Strange situation for sure. <code>selectedInstances.length</code> is showing as <code>1</code>, but the <code>mat-select</code> is still disabled. What am I doing incorrectly?</p>