Tax Account for PO Matched Invoices

Hi
I'm having trouble with the tax accounts that the system derives for PO Matched Invoices. Instead of accouting to the Expense Account setup in the tax rate in the EBtax module, the system is using the item account.

This is not happenig with invoices that are not matched to Po's, in these cases the tax account (non recoverable) is the one setup at the tax rate. I need this same result for invoices matched to PO's.

How can I do this?

Thanks
Alicia