Después de actualizar a RC5, comenzamos a recibir este error:

ngModel cannot be used to register form controls with a parent formGroup directive.  Try using
  formGroup's partner directive "formControlName" instead.  Example:


<div [formGroup]="myGroup">
  <input formControlName="firstName">
</div>

In your class:

this.myGroup = new FormGroup({
   firstName: new FormControl()
});

  Or, if you'd like to avoid registering this form control, indicate that it's standalone in ngModelOptions:

  Example:


<div [formGroup]="myGroup">
   <input formControlName="firstName">
   <input [(ngModel)]="showMoreControls" [ngModelOptions]="{standalone: true}">
</div>

Parece que en RC5 los dos ya no se pueden usar juntos, pero no pude encontrar una solución alternativa.

Aquí está el componente que produce la excepción:

<select class="field form-control" [formGroup]="form" [(ngModel)]="cause.id" [name]="name">
<option *ngFor="let c of causes" [value]="c.text">{{c.text}}</option>
</select>