             lines.removeChildAt(lines.numChildren - 1);
             separators.pop();
         }
+        UIComponentGlobals.layoutManager.validateClient(lines, true);
     }
     
      /**

            var c:DataGridColumn;

            var maxHeaderHeight:Number = 0;

            while (cols && colNum < cols.length)
            {
                c = cols[colNum];
                item = dataGrid.createColumnItemRenderer(c, true, c);
                rowData = new DataGridListData((c.headerText != null) ? c.headerText : c.dataField, 
                                                                c.dataField, colNum, uid, dataGrid, 0);
                if (item is IDropInListItemRenderer)
                    IDropInListItemRenderer(item).listData = rowData;
                item.data = c;
                item.visible = true;
                item.styleName = c;
                addChild(DisplayObject(item));
                var oldHeader:DisplayObject = headerItems[colNum];
                if (oldHeader)
                {
                    removeChild(oldHeader);
                }
                headerItems[colNum] = item;
                // set prefW so we can compute prefH
                item.explicitWidth = ww = c.width;

                sep = new UIComponent();
                sep.addChild(DisplayObject(sepSkin));
                lines.addChild(sep);
                UIComponentGlobals.layoutManager.validateClient(sep, true);
                
                separators.push(sep);
            }
