jQuery Grid Plugin - jqGrid

Hi,  there seems to be an issue with shrinkToFit or when horizontal scroll bar appears.

I'm having an issue the the grid when trying to use shrinkToFit to contains a large number of columns within the view.  This issue is only occurring in IE (Firefox works fine). 

Scenario: With subgrid to be displayed when clicking on the expanding + icon, wait until subgrid loads, move mouse, the subgrid will disappear.  Click on the row once or twice to highlight the row, the subgrid will appear again, hover order the parent row again, it disappears.

Is this something I'm not doing correctly?  The code looks like below (I trimed the columns down to make it simply but basically I have arnd 20 columns that needs horizontal scroll bar).

        $("#tb").jqGrid({       
            caption:"",
            url:"\\data.aspx",
            mtype:"POST",
         datatype:"json",
         postData:getPostData(),
         height:"100%",
         shrinkToFit:false,
            colNames:['C1'],
            colModel:[
                {name:'C1',index:'C1',hidden:true}
            ],
            pager:$('#nav'),
            pgbuttons:false,
            pgtext:false,
            pginput:false,
            viewrecords:true,
            sortname:'C1',
            sortorder:"asc",
            subGrid:true,
            subGridRowExpanded:function(subgrid_id, row_id) {
                var row=$('#tb').getRowData(row_id);
                var subgrid_table_id=subgrid_id+"_t";
                    $("#"+subgrid_table_id).jqGrid({
               url:"data2.aspx",
               postData:{ row:row.id },
                        mtype: "POST",
                     datatype: "json",
               colNames: ['S1'],
               colModel: [{name:"S1",index:"S1",width:60}]
                     width:600,
       height: '100%'
              }).navGrid();
            }
        });