title: Unable to set subscribe data of BehaviorSubject
body: <p>Trying with BehaviorSubject and 2 components. But not able to set the data receiving from subscribe.</p>
  
  <p><strong>Components A</strong></p>
  
  <pre><code>name:string = 'Test';
    constructor( private data: DataService) { }
    ngOnInit() {
      this.data.currentMessage.subscribe(val =&gt; this.name = val);
    }
  </code></pre>
  
  <p><strong>Component B</strong> (with text field)</p>
  
  <pre><code>name:string = 'Test';
    frm:FormGroup;
    constructor(private fb: FormBuilder, private data: DataService) { }
    ngOnInit() {
      this.setup();
      this.data.currentMessage.subscribe(val =&gt; this.name = val);
    }
    setup(){
      this.frm = this.fb.group({
        name:['']
      });
    }
    setData(){
      this.data.changeMessage(this.frm.get('name').value);
    }
  </code></pre>
  
  <p>on form submit setData() function is called.</p>
  
  <p><strong>Data Service</strong></p>
  
  <pre><code>private messageSource = new BehaviorSubject('default message');
    currentMessage = this.messageSource.asObservable();
    constructor() { }
  
    changeMessage(message: string) {
      this.messageSource.next(message)
    }
  </code></pre>
  
  <p><strong>On load:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/COjnU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/COjnU.png" alt="enter image description here"></a></p>
  
  <p><strong>On Submit form:</strong></p>
  
  <p><a href="https://i.stack.imgur.com/1VrpY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1VrpY.png" alt="enter image description here"></a></p>
  
  <p>Value is changing in Component B but not in A. Whats wrong in A that its not changing? Please Help.</p>