JqGrid key:true not working with field having custom formatter - jqgrid

Question

I have a grid with following options where "id" I want to set for a row need to be custom formatted.
There are two columns libCode and matCode.
Combining data of these two I want to create Id for row as follows:-
" ;libCode=[libcode];matCode=[matCode]"
But key=true option is not working with this field having its data set by custom formatter.
It returns the row no. if no xmlmap option is defined, or returns data from xmlmap element from XML response but not what custom formatter sets.
I want to know that why key option is not working and is there any other way I could implement this.
Here is my code for grid:
$(function () {
$("#list").jqGrid({
url: "./TestServlet?operation=RetrieveAll&accept=List",
datatype: "xml",
mtype: "GET",
colNames: ["Lib Code", "Mat Code", "Row Id"],
colModel: [ { name: "libCode", hidden:true, xmlmap:"libCd"},
{ name: "matCode", hidden:true, xmlmap:"matCd"},
{ name: "rowId", formatter:formatName , key:true}
],
xmlReader:{
root:"libs",
row:"lib",
repeatitems: false
},
pager: "#pager",
rowNum: 10,
rownumbers: true,
rowList: [10, 20, 30],
sortname: "libCd",
sortorder: "desc",
viewrecords: true,
gridview: true,
autoencode: true,
loadonce: false,
caption: "Library"
});
});
function formatName(cellValue, options, rowObject)
{
return " ;libCd="+$(rowObject).find('libCd').text()+";matCd="+$(rowObject).find('matCd').text();
}

Answer 1

Set property loadonce to true instead of false i.e. loadonce: true.