This behavior is intended as you don’t always want recurring template changes to automatically propagate to all invoices previously generated. This is to ensure the audit trail is maintained, if a client changes address you want the earlier invoices to reflect the old address and not to automatically update.
I agree in some cases it may be desirable to back-date changes but this can be quite intensive on our system, looping back through multiple invoices and applying updates.
We may possibly provide these options in the future but I’m afraid it’s not something on our near-term plan.