If you edit an Active receipt (not yet completed) and reduce the existing quantity of an item, this indeed posts a return on the receipt. The Receipt Audit List should show a negative quantity.

Where are you looking to see a positive amount? If it is the new Transaction History inquiry function, perhaps you are using an older version - there were a couple of transaction types that incorrectly displayed positive instead of negative, though everything posted correctly (including to the GL). These have since been fixed.

If you view the Items with Sales and Costs, do you see the correct inventory here?