Updating Po Line Items

I am trying to update po line items with a User Event, afterSubmit function. I can update values on the PO body, but not on the line items.  The script runs w/o error but the location field on the item does not change. Any ideas?

 unction afterSubmit(type){     if(type == 'create' || type == 'edit'){    var newType = nlapiGetRecordType();    var poId = nlapiGetRecordId();        var po = nlapiLoadRecord(newType, poId);    po.setFieldValue('custbodytesttext', "test");          var numOfLines = nlapiGetLineItemCount("item");      for (var i = 1; i <= numOfLines; i++) {                        nlapiSelectLineItem('item',i);                 var locationTxt = "test"                      nlapiSetCurrentLineItemValue("item", "location", locationTxt);           nlapiCommitLineItem("item");                     }              nlapiSubmitRecord(po, true);      }    }