Blanket Invoices
The functionality also applies to blanket invoices.
However, the exchange rates applied to the T&M entries on each job are determined by the invoices on account being reconciled on the individual job, not by the invoices on account being reconciled on the invoice as a whole.
If a blanket invoice contains contributions from drafts for both zero invoices and non-zero invoices, then this functionality only applies to the contributions from drafts for zero invoices.