If s?he's issuing a $dbh->disconnect; at the end of the say.. subroutine that does the inserts, it should commit the transactions. Issuing a $dbh->finish; (or was it $sth->finish; ?) before the disconnect may commit the records.
I currently use DBD::Sybase within mod_perl apps, but most of the time they are selecting rows from rather large tables vs inserting rows.