DataSource only fires once

gistfile1.js

MyApp.List = SC.Record.extend({

  name: SC.Record.attr(String)
  ,itemKeys: SC.Record.attr(Array)
  
  ,primaryKey: 'key'
  
  ,addItems: function(items){
    var refs = this.get('itemKeys') || new Array, 
        keys = items.getEach('key');
    keys.forEach(function(key){
      if(refs.indexOf(key) < 0){
        refs.push(key); 
      }
    }, this);
    this.set('itemKeys', refs);
  }
}) ;

This code is taking an array of records, and pushing their keys into this records array of itemKeys. This doesn't seem to fire the datasource, outside of the first call. Thoughts?