Ember (1.13.x) Async has many relationship is not serialized

I have model with hasMany relation:

User = DS.Model.extend 
departments: DS.hasMany 'department', async: true

Also the user's model has embedded relation and serializer (extends ActiveModelSerializer) has EmbeddedRecordsMixin.

To set has-many relations I use select-2 component. Relations set correct but when I save a record department_ids field is not passed to the server.

• Ember 1.13.8
• Ember Data 1.13.8

For Ember <= 1.10 it works fine