title: Async pipe not working with Subject
body: <p>I have the following BehaviorSubject in a service:</p>
  
  <pre><code>  isAuthenticated = new BehaviorSubject&lt;boolean&gt;(false);
  </code></pre>
  
  <p>And I am using it as follows in a component:</p>
  
  <pre><code>  authenticated: Observable&lt;boolean&gt;;
  
    constructor(private accountService: AccountService) { }
  
    ngOnInit() {
      this.authenticated = this.accountService.isAuthenticated.asObservable();
    }
  </code></pre>
  
  <p>And in the template I do something like :</p>
  
  <pre><code>  &lt;li class="login-button" *ngIf="!authenticated | async"&gt;
      &lt;a (click)="authenticate()"&gt;Log in&lt;/a&gt;
    &lt;/li&gt;
    &lt;li *ngIf="authenticated | async"&gt;
      &lt;a&gt;Logged in&lt;/a&gt;
    &lt;/li&gt;
  </code></pre>
  
  <p>The issue is that I dont see any of the two <code>li</code>, although the assumption is that the first one should appear since I am assigning the initial value of the Subject to false.</p>
  
  <p>What am I doing wrong?</p>