jQuery Grid Plugin - jqGrid

After search button clicked grid rownumber is from -19 to 0

how can i solve this problem?

<SCRIPT type=text/javascript>

    jQuery("#list").jqGrid({
           url: 'include/partsearch.php?Part=',
        datatype: "xml",
           colNames:["PartNo", ....],
           colModel:[....
           ],
           autowidth: true,
        rownumbers: true,
        height: 'auto',
          rowNum:20,
           rowList:[20,30,50],
           sortname: "partno",
        sortorder: "asc",
           viewrecords: true,
        viewsortcols: [true,'horizontal',false],
           pager: '#plist',
        caption:"Part List View"
    }).navGrid('#plist',{edit:false,add:false,del:false});

   
    $("#PNoSearch").click( function(){
        var SearchTxt = $("#SearchTxt").val().toUpperCase();
        $("#SearchTxt").val(SearchTxt);
        $("#list").setGridParam({url: "include/partsearch.php?Part=" + SearchTxt });
        $("#list").trigger("reloadGrid");
    });
</script>

<b>PartNo : </b><input type='text' id='SearchTxt' maxlength='16' size='20' />
<input type='button'  id='PNoSearch' value='Search'/>

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