Why is there use the Standard Cost from Item and not from Stockkeeping Units (for this specific - Variant Code)?

See scenario:

Set up the Inventory Setup:
- Automatic Cost Posting = TRUE
- Expected Cost Posting to G/L = TRUE
- Average Cost Calc. Type = Item & Location & Variant.

Use Item = 1001
- Costing Method = Standard
- Standard Cost = 100
- Replenishment System = Prod. Order
Create new Stockkeeping Units:
- Variant Code, Location Code
- Standard Cost = 10.
- Replenishment System = Prod. Order

Create new Prod. Order for this – Item, Variant Code, Location Code.
Use Output Journal to produce the Item (Inventory Account (Interim) = 10).

Run Change status (Finished) Prod. Order and then run Adjust Cost - Item Entries. After that:
- Inventory Account (Interim) = 0
- Inventory Account = 100

Why is there use the Standard Cost from Item and not from Stockkeeping Units (for this specific - Variant Code)?

If exist Stockkeeping Units for particular Item we suggest to use Standard Cost from Stockkeeping Units in all cases (for specific - Variant Code, etc.).