This is a common problem with programs using class::dbi in a persistent environment. It appears that although CDBI tries to do the right thing concerning object indexes, it is quite easy to get your scoping wrong on some objects, which leaves you with "old" objects in your process.

See http://www.class-dbi.com/cgi-bin/wiki/index.cgi?CommonProblems and DBI.pm#UNIQUENESS_OF_OBJECTS_IN_MEMORY for more discussion and solutions.