title: Ember-data removeObject on a hasMany relationship also removes the child entry from Ember's Store
body: <p>I have two models:</p>
  
  <pre><code>App.User = DS.Model.extend({
      firstName: DS.attr('string'),
      lastName: DS.attr('string'),
      phoneNumber: DS.attr('string'),
      studies: DS.hasMany('study', {async: true})
  });
  
  App.Study = DS.Model.extend({
      name: DS.attr('string'),
      description: DS.attr('string'),
  });
  </code></pre>
  
  <p>I want to un-assign some <code>Studies</code> from a <code>User</code>.<br>
  When the user presses the un-assign button in the view, there is an action inside the controller which runs this code: </p>
  
  <pre><code>actions: {
   //...
   unassign: function(study){
       this.get('user').get('studies').removeObject(study);
       this.get('user').save();
   }
   //...
  }
  </code></pre>
  
  <p>This removes the <code>studyId</code> from the <code>users.studies</code> list, but it also removes that <code>study</code> completely from Ember's store.</p>
  
  <p>How can I just un-assign the <code>study</code> from the <code>user.studies</code> , but keep the <code>studies</code> table unaffected.  </p>
  
  <p>I'm using: </p>
  
  <pre><code>Ember VERSION = '1.5.1';
  Ember-Data Version = 1.0.0-beta.6
  </code></pre>