I used a ready prepared client with no bookings either with accrual accounting and with cash based accounting (re importing same prepared database).

Facts:
Product: Pott: Cost 0, Stock 0, po price 3.29 EUR

I produced the same business incident:
Purchase order: 10x Pott a 3.29 EUR
Tax 19%
Grand Total: 39.51

MM Receipt:
10x Pott

Vendor Invoice:
10x Pott 3.29 EUR
1x Cost 7.10 EUR (same Tax)
Total: 40.00 EUR
Grand Total (including Tax): 47.60

Payment amount: 46.17 EUR, Discount Amount: 1.43

Resulting cost records on product:

Accrual accounting (correct values):
Standard Cost: 3.29
Average PO: 4.00

Cash based accounting:
Standard Cost: 3.29
Average PO: 2.58