In core Odoo the reference of an invoice (account.move.ref, label Customer Reference on customer documents) is not copied when the invoice is duplicated. This addon makes it copy, and warns the user afterwards.

How it works

Python (models/account_move.py): ref gets copy=True. copy_data() removes it again for every move that is not out_invoice / out_refund, so vendor bills and journal entries keep the core behaviour. An explicit ref in the default dict always wins (credit note reversal sets its own).
JS (static/src/js/duplicate_warning.js): patches FormController.duplicateRecord. After the duplicate, if the new record is an account.move customer invoice/credit note with a non-empty ref, a modal alert dialog (OK button) warning is shown: "'Customer Reference' was also copied, check whether it is still relevant or should be removed." (nl: "'Referentie klant' werd ook gekopieerd, kijk na of dit relevant is of dient verwijderd te worden.")

Scope

Only the Duplicate action in the form view shows the warning. Server-side copy() calls (e.g. recurring entries) copy the reference silently.
No warning when ref is empty.

Compatibility

Odoo 16.0 (Community and Enterprise)
Depends on: account

Credits

bv Domus La Vila — https://domuslavila.eu

License: LGPL-3