When a user wants to add a line to a sales order, it doesn't add to the end, instead it inserts above the last line (or whatever line they have selected). This is useful in the case of "billing only" orders that we use to correct incorrect pricing. We begin with a negative qty on an item, and then a positive qty with the correct price. Unfortunately, when posting the pack slip the receipt must process before the issue, so if the lines are out of order, then we have to post two pack slips. correcting the line sequence would avoid the workaround.