Unique Constraint Violation on Handler During Upgrade

Question

We followed directions for performing a new install of 11.6 and upgraded an old 10.1 database per infocenter guide. However, we receive errors during the database upgrade step running 'madconfig upgrade_virtual_mdm' target. Prior to the upgrade our table contents were perfectly valid according to the documentation and schema definition. However, upon attempting upgrade a change is introduced (a new unique index) that considers our data invalid and throw exceptions rather than attempting gracefully to deal with this possibility or at least written verbiage in infocenter explaining for this possibility and how to prepare for it prior to attempting an upgrade process. ERROR ODBC [23000] [InitiateSystems][ODBC SQL Server Wire Protocol driver][Microsoft SQL Server]The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.mpi_handler' and the index name 'mpi_handler1'. The duplicate key value is (com.cvw.handlers.PersonHandler). (DBError=1505)