I see this often if there is a misc item setup as a Stock item instead of a non-stock item and if you sell that misc item negative.  The system doesn't know the actual cost since there is a negative qty on hand so it will use the last cost.  Then when you do an inventory adjustment or receive in the same misc item it will try and correct itself as it had been using an estimated cost.  Add the Item ID column to the GL report you are looking at and then run the Item Costing Report and filter it for just that item.  That will give you a breakdown of what happened with the item.  It might be something you can fix by drilling into the transaction that adjusted or received the qty.  I can take a look at it as well if needed.  [email protected]