Wrong Product Cost Quantity if receipt quantity <> invoiced quantity

Costing method=Average PO

Product=>Costs=>Current Quantity is wrongly updated if the (matched PO) MR quantity does not exactly match with the (matched PO) invoiced quantity.
Below are 2 example scenarios:

SCENARIO 1:

Purchase Order Order Qty=100
Vendor Invoice(1) Qty=100
Partial MR(1) Qty=40
Partial MR(2) Qty=60

3 matched Purchase orders are created:
1.) Invoice Line Qty=100, Receipt Line=null (not posted because no MR assigned)
2.) Receipt Line Qty=40, Invoice Line=null (posted)
3.) Receipt Line Qty=60, Invoice Line=null (posted)

There are 3 issues here:

1.) When performing MR(1) with Qty=40, product cost quantity gets updated to 140 (100+40) instead of 40. When performing MR(2) with qty=60, product cost quantity gets updated to 200 (100+40+60) instead of 100.
2.) The system does not create matched invoices/receipts when recording MR(1) and MR(2)
3.) In the matched PO, the system does not allocate invoice lines to receipt lines. The system should assign a receipt line to the invoice line after each MR (according to matched invoice posting in 2.) which would look like this at the end:
Matched PO 1: Invoice Line1, Receipt Line1 Qty=40
Matched PO 2: Invoice Line1, Receipt Line2 Qty=60

SCENARIO 2:
Purchase Order Qty=100
Vendor Invoice(1) Qty=40
Vendor Invoice(2) Qty=60
Partial MR(1) Qty=40
Partial MR(2) Qty=60

When performing MR(1) with qty=40, product cost quantity gets updated to 100 (40+60) instead of 40.

There are many more combinations causing the above issues.