[Koha] Barcode Duplication Problem in Koha 2.9.9

Iam using Koha 2.9.9. on susi 10.1 I found that the Barcode is duplicated when the user is editing a record in the cataloging . Any barcode during this stage will be accepted in the database either in the database before or not. The command button for it is "save change" in the edit item/record in cataloging. That one is that record exits but try to change information about the record.  To Add a new it, the koha software block barcode duplication here.  The command button for it is Add Item. This block duplication of Barcodes. Can anybody help with the block if duplicated barcode in the "save change" under edit item Akin Adigun (MCP) Akinomatics Tel: 234 - 02-7512326, 08029219271