Ember-data removeObject on a hasMany relationship also removes the child entry from Ember's Store

I have two models:

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'),
});

I want to un-assign some Studies from a User.
When the user presses the un-assign button in the view, there is an action inside the controller which runs this code:

actions: {
 //...
 unassign: function(study){
     this.get('user').get('studies').removeObject(study);
     this.get('user').save();
 }
 //...
}

This removes the studyId from the users.studies list, but it also removes that study completely from Ember's store.

How can I just un-assign the study from the user.studies , but keep the studies table unaffected.

I'm using:

Ember VERSION = '1.5.1';
Ember-Data Version = 1.0.0-beta.6