R12 Recurring Invoices not calculating tax in invoce validation

 Currently looking into this issue but thought I'd check if anyone has any clues.

My client uses recurring invoices as well as invoices created from POs by Pay on Receipt. The issue I have is that if both types of invoice are validated, the tax is not calculated, no tax line is created, and the invoice total on the General tab excludes tax.

Early tests have indicated that if you go into Tax Details the tax lines are identified as being Manually Entered and the tax value is there! When you exit Tax Details the Tax line appears as if by magic and the total on the General tab includes  tax.