item groups & sublist line numbers

Hi folks,

    Newbie here.   Trying to write an assistant to help salespeople fill the item sublist on opportunities.  So I want this code to run while in edit mode.  Here's a very simple client-side code that illustrates my problem:

function testgroup(){

   nlapiSelectNewLineItem('item');
   nlapiSetCurrentLineItemValue('item','item',230,'false','true');
   nlapiCommitLineItem('item');

   nlapiSelectNewLineItem('item');
   nlapiSetCurrentLineItemValue('item','item',41,'false','true');
   nlapiCommitLineItem('item');

}

Works fine if the first item, item 230, is a regular item, but if 230 is a item group instead, it fails.  The item group is written/committed just fine, but the next item (41 in the example) isn't, at least not reliably. 

Inserting nlapiGetCurrentLineItemIndex suggests that the second nlapiSelectNewLineItem is pointing incorrectly to line 2 (as if the item group was a single item) - but I'm not sure if that is the cause or just another symptom.