I suppose that the problem exist because old data values will be not removed by
jQuery("#myJqGrid").jqGrid('setGridParam', { data: data });

The above code works good with empty data, but it could worrk wrong if another (old) data already exist. What you can do is setting the data array using getGridParam:

var referenceToInternalData = jQuery("#myJqGrid").jqGrid("getGridParam", "data");
referenceToInternalData

Hello.

I had the same problem and I solved it as follow:

jQuery('grid').jqGrid('clearGridData');
jQuery('grid').jqGrid('setGridParam', {data: dataToLoad});
jQuery('grid').trigger('reloadGrid');

Best regards.