Hello Koha-Mailinglist, in the meanwhile I was tying to find reasons for this strange behavior. First the good news: The Koha-generated EAN13-barcode in itself is correct. However: 1. All QR/barcode-code readers suppress the very first leading zero ONLY, if there is any. This leads to the problem, that sometimes it outputs only 12 instead of 13 digits. 2. All QR/barcode-code readers also print out the last check-digit. This leads to the error, that the Koha search function is not working, as the last digit is a check-digit, it is by the EAN13 definition not part of the payload-data and thus must not be a part of the assigned book/shelf-number. You may easily check this using a free QR-code reader on a smartphone (i.e. Lightning QR). I hope somebody is interested in this, because the labeling and serach functions are essentials parts of a professional library system. Best Regards Kamilla Braun