Double tax when matching Payables invoce to PO receipt

Hi

We are in R12 and we are using Financials +SCM modules

I have setup the tax using Tax Rules with Event Class Category :Tax Event Class and Event Class=Purchase Transaction.

Then I set up Application tax Options for Purchasing and  Payables.

For Purchasing the tax classification defaulting order is as below

1:Item

2:Supplier Site

For Payables

1:Supplier Site

When entering Purchase order  the tax code is defaulted correctly, however when we match the invoice to the PO receipt , we get 2 tax codes on the invoice, one is defaulted from the Item (from Purchasing application ) and the other tax codes is defaulted from Supplier site(from Payables Appl. Tax Option)