Tax on AGIS AP Transactions - why does Oracle try and bring the tax rate used for the AR transaction

We have an automated tax solutoin so when we create an AGIS transaction between 2 countries, we want the AR and the AP taxes to be independantly calculated and not import the tax rate from the AR transaction into the AP. WE are having major problems with one client because we calcaulte Germany VAT ont he AR transaction but when the intercompany AP transaction is creted for the French Operating unit, the system is trying to force the tax to be the same as that of the German OU - which is compeltely wrong and a massive failing by oracle.
We understand that this is caused by the workflow somehow trying to import the AR tax information into the AP interface but how do we turn this off? how can we remove this rubbish code from the workflow so that no tax information is brought across (except for the tax classicaiton code).