Fix for: https://github.com/emberjs/data/commit/829753e4cb66d6ac93bac5b9983ed7056633d266#commitcomment-4969509

ApplicationStore.addUnsavedRecords.fix.js

  didSaveRecord: function (record, data) {
    if (data) {
      this.didSaveRecordForHasManyItems(this, record.constructor, data, record);
    }
    this._super(record, data);
  },

  // Fixes introdution in ember-data.1.0.0.beta4 (see method "addUnsavedRecords" in Store)
  // assume that "any unsaved records that are
  // in a hasMany they won't be in the payload"
  // which could be not true if serializer handles child items
  didSaveRecordForHasManyItems: function (store, type, data, record) {
    var self = this;
    
    type.eachRelationship(function (key, relationship) {

      var kind = relationship.kind,
          value = data[key];

      if (value === null) { return; }

      if (kind === 'hasMany') {
        record.get(key).forEach(function (childRecord) {
          childRecord.adapterWillCommit();
          childRecord.adapterDidCommit();
          self.didSaveRecordForHasManyItems(store, childRecord.constructor, {}, childRecord);
        });
      }
    });

    return data;
  },