Our system is set up to use FIFO for Costing Method and Automated for Inventory Valuation.   Assume we have 10 items in stock at a cost of $1 each.  We created a PO for another 10 items, applied the new cost of $10 each, and completed receiving.  Realising the mistake, we attempted to return those 10 items at the higher cost price.  We noticed Odoo returned the first 10 items that we had in stock instead of applying the return to the PO.  This caused the cost of the existing goods to be at the $10 value.

1. Is this a bug in the system?
2. If not, what's the proper way to fix this issue without affecting the COGS and/or the Inventory Valuation?

Thank you!