VAT calculation on a Payables invoice created through the projects billing intercompany process

Summary

How is VAT calculated on a Payables invoice created through the projects billing intercompany process

Content

Does anyone have any documentation on how tax should be calculated on a Payables invoice created through the projects billing intercompany process?

In short: Projects Intercompany Billing creates both an AR and an AP transaction.

Note: both legal entities fall under the same tax regime

We expect that both transactions will follow the tax rules that have been setup, but it seems that it is only using those rules for the AR transaction and not for the AP transaction.  It looks like that on the AP transaction it is using the same tax code as on the AR transaction.  Through the tax rules it should default a different one.  That's also what happens when we use the tax simulation.