Error for one hasMany but not another. Makes no sense - ember.js

Question

I have a model "Group" that has some hasMany relationships "members" and "links". I have a controller that adds a new group but i get the following error on save
"Assertion Failed: A App.Group record was pushed into the store with the value of links being '{}', but links is a hasMany relationship so the value must be an array. You should probably check your data payload or serializer."
I can fix this by returning an empty links array in the response json but i don't necessarily want this included and i don't understand why i get this error for links but not for members as that isn't included in the response either.
App.AddGroupController = Ember.ObjectController.extend({
needs: ['application'],
actions: {
submitForm: function(){
var self = this;
var model = this.get('model');
self.send('showLoading', 'Saving');
model.save().then(function(){
self.send('hideLoading');
//Go to the groups list
self.transitionToRoute('groups');
},function(error){
self.send('hideLoading');
console.log(error);
//Must supply reject callback, otherwise Ember will throw a 'backend rejected the commit' error.
});
}
}
});
App.AddGroupRoute = App.AuthenticatedRoute.extend({
model: function(){
return this.store.createRecord('group');
}
});
App.Group = DS.Model.extend({
title: DS.attr('string'),
description: DS.attr('string'),
members: DS.hasMany('groupMember'),
links: DS.hasMany('groupLink'),
});
App.GroupLink = DS.Model.extend({
title: DS.attr('string'),
link: DS.attr('string'),
});
App.GroupMember = DS.Model.extend({
first_name: DS.attr('string'),
last_name: DS.attr('string'),
email: DS.attr('string'),
profile_picture: DS.attr('string'),
});
Response from save:
{
"group":{
"id":26,
"title":"Test Group",
"description":"Dummy group description",
}
}
Im using:
Ember : 1.9.1
Ember Data : 1.13.14