Thank you for looking into this.
I think I understand, but is still strange because I never generated invoices before 1 month ago (in the order statuses > invoice column all the orders were UNselected).
Infact I think the issue began when I selected an order status to generate invoices the first time, maybe it's the same thing that you are saying.
What you should do then is to run a mass action to set the order_invoice_created with the value of order_modified and the order_invoice_id with the value of order_id.
mmmh... not sure how to do this. I do see the action option "update values" in mass action, but it seems it requires some coder expertise to run that correctly.
see:
www.screencast.com/t/1Ohe12SvXxw