Entity Framework & WPF - When is a dbContext.Load() required?

QUESTION

Main Question With a WPF application that is using a single dbContext across multiple windows; is a dbContext.Load() required for each window that creates a CollectionViewSource? If its not required, then how do you get around it?

If this question isn't clear, i've created a simple example in hopes to demonstrate. Below i've created a small simplified example.

I ask this because i am looking to reduce window loading times and i though this may be the case. If there is a local cache of some sort, by doing a load for every window am i causing a performance hit?

Follow On Question If it is not, is some sort of include required in the main window to load relational parts?

EXAMPLE

A WPF Application using a MainWindow, declares a dbContext "MyDbType"; which remains open while each NewSubWindow uses .ShowDialog() to open. Each new window is passed the dbContext. All windows declare a CollectionViewSource in their XAML.

The Db Definition

//The context
public class MyDbType : DbContext
{
    public DbSet<MyType1> MyTable1 { get; set; }
    public DbSet<MyType2> MyTable2 { get; set; }
}

// The main type
public class MyType1
{
    public int Id { get; set; }
    public string Tag { get; set; }
    public virtual ObservableCollection<MyType2> BunchOf2s { get; set; }
}

// A relational sub type
public class MyType2
{
    public int Id { get; set; }
    public string Name { get; set; }
    public virtual MyType1 MyParent { get; set; }
}

The WPF Main Window

public partial class MainWindow : Window
{
    public MyDbType db = new MyTypeDb();
    ....
    ...
    ...

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        myDb1ViewSource = ((CollectionViewSource)(this.FindResource("myDb1ViewSource")));
        db.MyTable1.Load();
        myDb1ViewSource.Source = db.MyTable1.Local;
    }

    public OpenNewWindow()
    {
        NewSubWindow newWin = new NewSubWindow(db);
        newWin.Owner = this;
        newWin.ShowDialog();
    }
}

A SubWindow

public partial class NewSubWindow : Window
{
    private MyDbType db;

    public NewSubWindow(MyDbType Db)
    {
        db = Db;
    }

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        myDb1ViewSource = ((CollectionViewSource)(this.FindResource("myDb1ViewSource")));
        db.MyTable1.Load(); // ----- DOES THIS SECOND WINDOW NEED THIS? OR IS IT JUST SLOWING THINGS DOWN?
        myDb1ViewSource.Source = db.MyTable1.Local;
    }
}