Observing RecordArrays in EmberJS

I have this setup right now:

App.Workspace = Em.Object.extend({
  users: null,
  usersChanged: Em.observer('users',function() {
    console.log('Users Updated!');
  }),
  ...
  initListeners: function() {
    var self = this;
    someObject.on('someEvent', function() {
      ...
      console.log('before set');
      self.set('users', self.store.all('users'));
    });
  }
});

I only get the output "before set", but not "Users updated!"

What am I missing?