If the invoice has items, perhaps you have such items associated with an account code that is cogs instead of an income account. Change the associated account , on the item list. Then refresh the item inside the offending invoice. Gary
As Kris has explain Jonathan - this is how inventory items work - when you purchase the stock - it goes to your Balance Sheet Asset account for Stock on Hand (DR entry) .... as each items is sold - the cost of the item reduces the stock on hand balance (CR entry) and increases your Cost of Goods sold account (DR entry)... this happens in the background of the tax invoice for the sale - so the entries you are seeing are the ones that should be there... Provided you have setup your inventory items correctly and are purchasing them correctly with their unit prices etc - then all will be well.