nlapiSetLineItemValue does not update the last line item

Hi,

I am having a strange issue with a very simple piece of code.  The script goes thru each line item and updates a custom column field.  It works very well except for the last line, where the custom field does not get populated.  I had an alert just before the nlapiSetLineItemValue and it does display the right cost_amount. 

Any ideas what could be going wrong here?  Thanks!


Extract:

for ( i = 1; i <= line_count; i++)
{
nlapiSelectLineItem('item', i);
var cost_amount = parseFloat(nlapiGetLineItemValue('item', 'amount',i)) * cost; 
nlapiSetLineItemValue('item','custcolusd_amount',i,cost_amount);
}