As reported by here:
https://groups.google.com/d/msg/idempiere/w9F_-lf1Loo/6fYdImJkDgAJ

Hi Carlos,

I just simulated a MR (DocNo=10000512) and an Invoice (Doc. no = 10000013) with price variation for product "Planting" of type=Service in your demo system https://demo.globalqss.com/webui/index.zul.
Can you please have a look at matched invoices doc=10000000. It shows that the variation is posted to the Inventory GL Account.
I thought that for products of type service any price variation would always get posted to Product Expense but it seems to go back to Product Asset.
Or is it required to change Accounting tab=>Product Asset to be an expense account for products of type Service?

Thanks,
Michael