MAJOR PROBLEM WITH \'QTY IN STOCK\'

MAJOR PROBLEM WITH \'QTY IN STOCK\'

Hi,
if you create an invoice then go back in, edit, and resave, the system deducts the product amounts again, creating false numbers in stock.
EG I sell 20 x Widget 1's. There are 100 in stock. I save the invoice and the new total in stock is 80. I need to add an address detail, so go back in, edit, and resave it. When you look at the resaved invoice, it will only show 60 in stock ???

Pls advise what to do ASAP.
Burnard Tauranga