title: What causes the "control.registerOnChange is not a function" error
body: <p>I have a form using the reactive form approach. The form is created as follow in my pug:</p>
  
  <pre><code>form([formGroup]='form', novalidate='', (ngSubmit)='postSurvey(form.value, form.valid)')
  </code></pre>
  
  <p>Everything works fine except when I try to change the form (which is a <code>FormArray</code>) in the javascript part. I get the following error:</p>
  
  <pre><code>EXCEPTION: Error in http://localhost:8080/app/components/fillForm.template.html:0:326 caused by: control.registerOnChange is not a function
  core.umd.js:3497 TypeError: control.registerOnChange is not a function
      at setUpControl (http://localhost:8080/node_modules/@angular/forms/bundles/forms.umd.js:1634:17)
      at eval (http://localhost:8080/node_modules/@angular/forms/bundles/forms.umd.js:4752:25)
      at Array.forEach (native)
      at FormGroupDirective._updateDomValue (http://localhost:8080/node_modules/@angular/forms/bundles/forms.umd.js:4747:29)
      at FormGroupDirective.ngOnChanges (http://localhost:8080/node_modules/@angular/forms/bundles/forms.umd.js:4616:22)
      at Wrapper_FormGroupDirective.ngDoCheck (/ReactiveFormsModule/FormGroupDirective/wrapper.ngfactory.js:30:18)
      at View_FillFormComponent2.detectChangesInternal (/AppModule/FillFormComponent/component.ngfactory.js:275:32)
      at View_FillFormComponent2.AppView.detectChanges (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12592:18)
      at View_FillFormComponent2.DebugAppView.detectChanges (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12739:48)
      at ViewContainer.detectChangesInNestedViews (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12850:41)
      at CompiledTemplate.proxyViewClass.View_FillFormComponent0.detectChangesInternal (/AppModule/FillFormComponent/component.ngfactory.js:64:14)
      at CompiledTemplate.proxyViewClass.AppView.detectChanges (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12592:18)
      at CompiledTemplate.proxyViewClass.DebugAppView.detectChanges (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12739:48)
      at CompiledTemplate.proxyViewClass.AppView.internalDetectChanges (http://localhost:8080/node_modules/@angular/core/bundles/core.umd.js:12577:22)
      at CompiledTemplate.proxyViewClass.View_FillFormComponent_Host0.detectChangesInternal (/AppModule/FillFormComponent/host.ngfactory.js:29:19)
  </code></pre>
  
  <p>My code to change the form is quite complex and I can't simplify it or reproduce it in a plunker. More than finding directly the solution (it's too difficult with so little details), I would like to understand what this error means? And what might cause this error.</p>
  
  <p>I have figured out that the error occurs at <code>[formGroup]='form'</code> in my HTML.</p>
  
  <p>Any suggestion will help.</p>
  
  <p><strong>Update</strong> I have filed an issue on angular github <a href="https://github.com/angular/angular/issues/26998" rel="noreferrer">here</a> and have proposed a fix <a href="https://github.com/angular/angular/pull/27246" rel="noreferrer">here</a> The plunker to reproduce the issue is <a href="http://next.plnkr.co/edit/vh1HCo2WrwNgr95G?open=lib%2Fapp.ts&amp;deferRun=1" rel="noreferrer">here</a></p>