Set::Object only deals with sets of Perl objects. It does not look inside the objects, or ask the objects if they are the same object as another object. Two references to objects, either refer to the same object or to two different objects.

The problem is that Class::DBI is providing multiple distinct Perl objects if a row is read twice, both of which encapsulate the same data. This, Set::Object cannot be aware of without defeating its own stated goals.

Perhaps you are using a database abstraction layer as if it were an object persistence layer.