To repriduce:
- Add a grid with Office2007Theme applied and sort by one of the columns
- Set RightToLeft to true
- Make sure the column width is no wider than the text

Workaround:
        void radGridView1_ViewCellFormatting(object sender, Telerik.WinControls.UI.CellFormattingEventArgs e) 
        { 
            GridHeaderCellElement headerCell = e.CellElement as GridHeaderCellElement;   

            if (headerCell != null) 
            { 
                if (radGridView1.ThemeName == "Office2007Silver" && e.Column.IsSorted) 
                { 
                    headerCell.Arrow.Alignment = ContentAlignment.TopCenter; 
                    headerCell.Arrow.Margin = new Padding(0, 1, 0, 0); 
                } 
            } 
        }