Not sure but I guess that's because in your former pattern you were creating a NEW CollectionView each time you called PersonsView.

Interesting enough if I expose this from Firm class:  

public List<Person> People { get { return people;} set { people = value;}}

public CollectionView PersonsView { get; set ; }

and change the constructor to this :

      public Window1()

      {

        InitializeComponent();

        var firm = new Firm();

        firm.PersonsView = new CollectionView(firm.People);

        layout.DataContext = firm;

      }

it actually works...go figure !

Thank you for your sample projects, seems to work fine. But getting closer to my model and using your Person & Jobs classes I've created a higher level class Firm:  

public class Firm

  {

    private List<Person> people;

    public Firm()

    {

      people = new List<Person>();

      for (int i = 0; i < 5; i++)

      {

        Person p = new Person();

        p.Name = "Name " + i;

        List<Jobs> j = new List<Jobs>();

        j.Add(new Jobs() { Title = p.Name + " Title" + i });

        j.Add(new Jobs() { Title = p.Name + " Title" + i });

        j.Add(new Jobs() { Title = p.Name + " Title" + i });

        p.Jobs = j;

        people.Add(p);

      }

    }

    public CollectionView PersonsView { get { return new CollectionView(people); } set {  } }

  }

changed the Window constructor to :

        public Window1()

        {

            InitializeComponent();

            layout.DataContext = new Firm();

        }

and the bindings to:

DataSource="{Binding Path=PersonsView, Mode=TwoWay}"

DataSource="{Binding PersonsView/Jobs}" 

...bang! no more syncronization...why ?

I am attaching a working sample project with this. Please point out where is the difference between the two scenarios.