Wrong posting on purchase process with item type service

When you make a purchase order for a product type service, in a fresh Idempiere installation using the garden world client, (I made it on my own installation and also I made it on the Global QSS demo site) and then you complete this document it doesn't generate any posting to the accounting. Then you make a material receipt (you create lines from the purchase order) and then you complete the document. The accounting facts for the material receipt are:
DB Product expenses
Cr Not invoiced receipts
Then you create the vendor invoice (you create the invoice lines from the receipt or purchase order) and complete the document. The accounting facts for the AP invoice are:
DB Product expenses
Cr Vendor liability (Accounts payable)
As you can see, the process has made two debits to product expenses, this is the BUG.

This bug can be fixed, changing the material receipt or the AP invoice accounting facts, but I think it's more accurate fixing the material receipt posting, it can be done if you make a DB and a Cr to a not invoiced receipts, the net result will be zero and all is right now, because for many cases the posting result of services receipt should be zero.