Workaround: 

        RadImageShape hint;

        protected override void OnLoad(EventArgs e)
        {
            base.OnLoad(e);

            InitializeComponent();

            hint = radGridView1.TableElement.RowDragHint;
            new Windows7Theme();
            radGridView1.ThemeName = "Windows7";

            radGridView1.TableElement.RowDragHint = hint;
          }