groupingGroupBy grouping recoirds by a column when i edit one record of the group change that cell value on all records of the same group, maybe the rowid is the same for all records on the same group?

$('#showData').jqGrid('setGridParam', { grouping:true });
$('#showData').jqGrid('groupingGroupBy',['PField'], { groupColumnShow: [false], groupDataSorted: true, groupCollapse: true} );
var firstGroup = $('#showData').find('tr.jqgroup:first');
$('#showData').jqGrid('groupingToggle', firstGroup[0].id);

and on ajax method:

onSelectRow : function(id) {
                var $this = $(this);		//this is the grid $('#showData')
                if (id) {
                  if (id !== lastSelCmp) {
                     $this.jqGrid('restoreRow', lastSelCmp);
                     $this.jqGrid('editRow', id, true);
                     lastSelCmp = id;
                  } else {
                     $this.jqGrid('restoreRow', lastSelCmp);
                     lastSelCmp = "";
                  }
               }

any ideas?