I would like to add additional information to my query above.

I just restored another invoice from history as a credit note. This time, I changed the "new" Credit Note number to a different number than it automatically creates when restored. The original invoice, and the credit note are included in the history report in this case. I suspect then that the error occurs when restoring an invoice as a credit note and we don't change the number. I'm confused then, why it would automatically default to that number. Am I missing something?