ArrayComputed: Groupby and computed properties not resolved from promises - ember.js

Question

I have a group model that contains some bets from several user. Every user can have more than one bet. In order to display the end result I want to group the bets by user and then sum up the points. this is my bet model that contains the point logic:
App.GameBet = DS.Model.extend({
scoreT1: DS.attr(),
scoreT2: DS.attr(),
betRound: DS.belongsTo('betround'),
game: DS.belongsTo('game', {async:true}),
user: DS.belongsTo('user', {async:true}),
points: function(){
var game = this.get('game');
var sc1 = this.get('game.scoreT1');
var sc2 = this.get('game.scoreT2');
var b1 = this.get('scoreT1');
var b2 = this.get('scoreT2');
if(sc1 == b1 && sc2 == b2) {
return 7;
} else if ((sc1 - sc2) == (b1 - b2)) {
return 5;
// Exakte Punktzahl
} else if ((sc1 - sc2) * (b1 - b2) > 0) {
return 3;
// Tendenz
} else {
return 0;
}
}.property('scoreT1', 'scoreT2', 'game.scoreT1', 'game.scoreT2')
});
This is working perfectly fine when I just render all bets with their points. But when I am using my own groupby ArrayComputeed function, it isn't working:
App.betGroupBy = function (dependentKey) {
var options = {
initialValue: Ember.A([]),
initialize: function (array, changeMeta, instanceMeta) {
return instanceMeta.previousKeys = {};
},
addedItem: function (accumulatedValue, item, changeMeta, instanceMeta) {
console.log(item.get('id') + " " + item.get('points'));
var user = item.get('user');
var key = user.get('id');
var group = accumulatedValue.findBy('key', key);
if (!group) {
group = Ember.Object.create({
key: key,
user: user,
bets: Ember.A([]),
betPoints: Ember.computed.mapBy('bets', 'points'),
points: Ember.computed.sum('betPoints')
});
accumulatedValue.pushObject(group);
}
group.get('bets').pushObject(item);
instanceMeta.previousKeys[Ember.guidFor(item)] = key;
return accumulatedValue;
},
removedItem: function (accumulatedValue, item, changeMeta, instanceMeta) {
var key = item.get(property);
var group = accumulatedValue.findBy('key', key);
if (!group) {
return;
}
var userBets = group.get('bets');
userBets.removeObject(item);
if (userBets.length === 0) {
accumulatedValue.removeObject(group);
}
return accumulatedValue;
}
};
return Ember.arrayComputed(dependentKey, options);
};
Somehow my "points" in the grouped function are always zero.
It seems that the promises are not early enough resolved or something.