As I see the sort does not depend on the grid, but in your script server side.

Regards

solved by setting rowNum to 1000

   I have a following grid:

$("#reportTable").jqGrid({
 url:'someUrl',
datatype: "json",
colNames:['Error count','Object', 'System', 'Error Code','Direction','Description'],
colModel:[
{name:'count',index:'count', width:45, sorttype:"int", fixed: true},
{name:'object',index:'object', width:120, fixed: true},
{name:'system',index:'system', width:100, fixed: true},
{name:'errorCode',index:'errorCode', width:120, formatter: formatLink, key: true, fixed: true},
{name:'direction',index:'direction', width:200, fixed: true},
{name:'description',index:'description', width:80}
],
rowNum:-1,
sortname: 'count',
sortorder: "desc",
loadonce: true,
caption: "Result",
cellEdit: false,
autowidth: true,
height: "auto",
ajaxGridOptions: { timeout: 30000 },
postData: {
fromDate: function() {return $('#fromDate').val()},
fromTime: function() {return $('#fromTime').val()},
toDate: function() {return $('#toDate').val()},
toTime: function() {return $('#toTime').val()}
},
jsonReader : {
root: "errorReportModel",
repeatitems: false
}
});

The problem is that after sorting one row is missing. When first loaded everything is ok. But after sorting last row (different row depending on the sort condition) is always missing. It is purely display problem because this row is displayed when you change sort order again (but other is missing). I am using JQ 1.6.4 and newest jqGrid, but it is the same on JQ 1.5.2.