Thanks for that bug report! When duplicating an invoice, not all properties of it will be carried over to the new invoice. For example, the invoice state will always be set to "Draft/Entwurf" on the new invoice, the invoice date will be set to "today" and the due date will also be adjusted accordingly. And of course, the invoice number can also not be duplicated, since it has to be unique.
However, you are right with having the expectation that "Salutation/Anrede" and "Payment terms/Zahlungsbedingungen" are being carried over from the invoice being duplicated (and not taken from the last present invoice). This will be fixed in the next app update. The same will happen with the "Currency/Währung". Buyer name & address are already copied over correctly in the current version, so no changes there.
Hope this updated behavior is what you are expecting the "Duplicate" action to do.
