I did have a similar problem that was very much like this. Using Dumper against $sth/$dbh is normally futile because the data is hidden behind a tie(). In cases of subclassing Perl's DBI, you'll laugh, you'll cry, and you may want to consider callbacks instead.
http://search.cpan.org/~timb/DBI/DBI.pm#Callbacks
Ken, I'll go back to the Perl DBI question I had previously and post what worked for me.