Incorrect COG after an Order was Cancelled

I have had an order cancelled, and the items returned to stock. The expected cost of goods is not reflected accurately after this transaction. How does the plugin handle cancellations/ refunds where the item is returned to stock/inventory?

Also, for the ATUM Inventory compatibility:

1. When a purchase order is created in ATUM I enter the qty and the total cost of those items e.g. 8no, $40 total…ATUM auto calculates the unit cost, but does not actually set the purchase price unless I click the button to “Set purchase price”, and if i dont set the purchase price on ATUM it doesn’t auto populate on the PO for me to know if the cost has changed the next time around. Is there a way that you can use the unit price calculated on the PO without me having to “Set purchase price”
2. When i have the ATUM Compatibility turned on it does update the quantity but if the stock is 0 it doubles it up, if it has stock it adds the new stock, then reduces the previous stock, but still somehow has the correct amount of stock expected.
3. The cost update is the issue, because if i do “set purchase price” it REPLACES the purchase price instead of using it to calculate the average cost of goods.

I am thinking that ATUM should update the Add Stock Table with the Stock and Cost as per the ATUM PO then use this table to calculate the cost$. The setting for Empty cost field can then come into effect if I use ATUM and the cost price there is 0, or I simply add stock without entering a cost price.