You cannot save the current row by performing the DataContext's SaveChanges method when the RadGridView is bound to IQueryable.

The code should look like this to work properly:
protected sealed override void BindingNavigator_SaveAction(object sender) {
    try
    {
        this.countriesRadGridView.EndEdit();
        BindingSource bs = this.countriesRadGridView.DataSource as BindingSource;
        bs.EndEdit();
        this.DataContext.SaveChanges();
        base.FireUpdateData();
    }
    catch (Exception Ex)
    {
        string exMessage = Ex.Message;
        MessageBox.Show(exMessage);
    }
}