dupes for PK and other UNIQUE indexes

Hi all;

I have a client with a table which has an exeedingly large amount of bloat, so
we plan to rebuild the table. However in setting up a test box I've found
that both the PK and another UNIQUE index column have duplicate values.

In theory the INDEX/PK should refuse to build if dupes exist on the data, and
subsequent data should refuse to load if the PK/UNIQUE index already exists.

Anyone have any Idea how this could happen?

Thanks in advance