grid 显示不正常，请指教！

Question

后台response的JSON数据如下（共18条）：{"total":18,"swjglist":[
   {"swjg_dm":"14200000000","swjg_jc":"省局"},
   {"swjg_dm":"00000000000","swjg_jc":"总局"},
   {"swjg_dm":"14213000000","swjg_jc":"市局"},
   {"swjg_dm":"14213020000","swjg_jc":"区局"},
   {"swjg_dm":"14213020100","swjg_jc":"东城分局"},
   {"swjg_dm":"14213020200","swjg_jc":"南郊分局"},
   {"swjg_dm":"14213020300","swjg_jc":"淅河分局"},
   {"swjg_dm":"14213020400","swjg_jc":"厉山分局"},
   {"swjg_dm":"14213029100","swjg_jc":"稽查局"},
   {"swjg_dm":"14213920000","swjg_jc":"市稽查局"},
   {"swjg_dm":"14213980000","swjg_jc":"开发区局"},
   {"swjg_dm":"14213770000","swjg_jc":"车购办"},
   {"swjg_dm":"14213810000","swjg_jc":"广水市局"},
   {"swjg_dm":"14213810100","swjg_jc":"应山分局"},
   {"swjg_dm":"14213810200","swjg_jc":"广水分局"},
   {"swjg_dm":"14213810300","swjg_jc":"马坪分局"},
   {"swjg_dm":"14213819100","swjg_jc":"广水稽查局"},
   {"swjg_dm":"14213900000","swjg_jc":"直属分局"}
   ]
}
JSP页面如下:
<script type="text/javascript">
Ext.onReady(function(){  var results = new Ext.data.Store({
    proxy: new Ext.data.HttpProxy({url:'${pageContext.request.contextPath}/queryAction.do?action=queryByDw'}),
    reader: new Ext.data.JsonReader({
    totalProperty:'total',
    root:'swjglist'
     },[
     'swjg_dm','swjg_jc'
     ])
  });  //定义一个grid
 var sm = new Ext.grid.CheckboxSelectionModel();
 var cm = new Ext.grid.ColumnModel([
        new Ext.grid.RowNumberer(),
        sm,
        {header:'机关代码',dataIndex:'swjg_dm'},
        {header:'机关名称',dataIndex:'swjg_jc'}
         ]);
  cm.defaultSortable = true; var grid = new Ext.grid.GridPanel({
        ds: results,
        cm: cm,
        sm: sm,
        title: '.',
        bbar: new Ext.PagingToolbar({
            pageSize: 10,
            store: ds,
            displayInfo: true,
            displayMsg: '显示第 {0} 条到 {1} 条记录，一共 {2} 条',
            emptyMsg: "没有记录"
        }),
        tbar: new Ext.PagingToolbar({
            pageSize: 10,
            store: results,
            displayInfo: true,
            displayMsg: '显示第 {0} 条到 {1} 条记录，一共 {2} 条',
            emptyMsg: "没有记录"
        })
    });
    grid.render('div-form');   results.load({params:{start:0,limit:10}});
});
</script>
为什么IE显示时在grid的tbar和bbar中的行距只有一行，而不是10行，里面有18条记录，可以翻着看。把数据源换成数组就显示正常。是我的JSON数据格式有问题，还是JSONReader写的有问题？请指教！