nlapiCommitLineItem problem

When commiting a line item in a client-side script with nlapiCommitLineItem('type'), the line commits, but not quite totally. If an additionnal item is added after having previously commited one by script (in seperate execution, I'm not talking about the asynch problem), the new item being added crushes the old one instead of going on a new line.

Here is some sample code, though there is noting special to it:

 varShippingLineItem = trim(calculateShipping()); //receives the name of the item to be added      //Select new line item  nlapiSelectNewLineItem('item');    nlapiSetCurrentLineItemText('item','item', varShippingLineItem, false);  nlapiCommitLineItem('item'); 

If this code is called again, it will crush the previously added line item instead of making a new line, unless the user manually goes in and presses "add" or selects another line.