property IsExpandable doesn't work correct

[Konstantin]

I am using a RadTreeListView and MVVM pattern. When I expand new item in my tree some items lost their expanders. 
 private void RadTreeListView_RowLoaded(object sender, RowLoadedEventArgs e)
        {
            TreeListViewRow row = e.Row as TreeListViewRow;

 if (row != null)
            {
                row.IsExpandable = !((TreeNodeViewModel)row.DataContext).IsEmpty;
            }
        }

TreeNodeViewModel - it's an item of tree.