Nuno
As a workaround, please modify your getData method.
getData: function (dataJSON) {
var data = dataJSON.data;
if(!data || !data.length){
var that=$(this).pqGrid("getThis").that;
that.dataGM=null;
}
return {
curPage: dataJSON.curPage,
totalRecords: dataJSON.totalRecords,
data: data
};
}