flex 中dataGrid绘制问题

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" 
layout="absolute" width="100%" height="100%">
<mx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
import mx.validators.NumberValidator;
import mx.events.AdvancedDataGridEvent;
import flash.events.MouseEvent;
import mx.events.FlexEvent;
[Bindable]
private var dataSource:ArrayCollection = new ArrayCollection([
{tjfl:'车间'},{xh:'1',tjfl:'外协'},{tjfl:'小计'},
{tjfl:'车间'},{xh:'2',tjfl:'外协'},{tjfl:'小计'},
{tjfl:'车间'},{xh:'3',tjfl:'外协'},{tjfl:'小计'},
{tjfl:'车间'},{xh:'4',tjfl:'外协'},{tjfl:'小计'},
{tjfl:'车间'},{xh:'5',tjfl:'外协'},{tjfl:'小计'},
{tjfl:'车间'},{cpbh:'总计',tjfl:'外协'},{tjfl:'小计'},
{xh:'简要说明'}
]);
]]>
</mx:Script>

<mx:AdvancedDataGrid id="dg1" designViewDataType="flat" sortExpertMode="true" sortableColumns="false" rowCount="5" dataProvider="{dataSource}" height="515" width="652" fontSize="14" fontFamily="Times New Roman" editable="true" horizontalScrollPolicy="auto" verticalScrollPolicy="auto" horizontalCenter="0" verticalCenter=