How can I serialize hasMany relations with ember-data > beta15?

Until ember-beta 14, everything was going fine. I have goal and account models.

goal hasMany('account'), but account does not have or belongs to goals (not on ember, there are no reason on my app.

With a custom serializer, I had all working fine:

//serializers/goal.js

    import DS from 'ember-data';

    export default DS.ActiveModelSerializer.extend(DS.EmbeddedRecordsMixin, {
      attrs: {
        account: { serialize: 'ids' }
      }
    });

my post request had all I need:

...
  account_ids: [1, 2, 3]
...

now I just have account_ids: []. Ember nows about my serializer, otherwise I would just have accounts, not account_ids on the request.

I tried all possible combinations from docs, with and without {async: true}, etc, nothing works.

What am I'm doing wrong?

I feel that it has something to do with the new snapshots api, but couldn't find any clue about how to work with it.

Thanks!