Tax Rule using event class 'Prepayment Invoice' AP only getting applied to unmatched lines

Summary:

Have created Direct Tax Rate Rule with Event Class = Prepayment Invoice.

If I create the Prepayment line manually, without matching to PO, rule is invoked and correct tax rate is applied - all good

If I create the prepayment line by matching to PO, rule is not invoked, I get a rate defaulted by some other rule. This is incorrect. On same transaction I am getting different behavior.

Some additional information (may or maynot be useful)

Can see the 2 line ap_invoice_lines_all matched lines get different values for field trx_business_category. Matched line = PURCHASE_TRANSACTION unmatched line = PURCHASE_PREPAYMENTTRANSACTION