Check uniqueness as defined in QBMUniqueGroup - QBMXUSer


I performed the consistency check by designer tool and I get the following error: Check uniqueness as defined in QBMUniqueGroup.
The error arise because two entry in the QBMXUser table with the same Ident_QBMXUser. I do not remember inserting the two entries neither changing the QBMUniqueGroup.
How is it possible that there are two entries with same Ident? Shouldn't object layer deny to insert the new value with same ident_qbmxuser?
Moreover, can I delete one of the two entries? Who inserts the values in that table (QBMXUser) and when does it happen? Is it related to XUserInserted and XUserUpdated attribute of all tables?

Version 8.1.3