I've found that post which seems to bring some sense: http://stackoverflow.com/questions/3952242/dbi-database-handle-with-autocommit-set-to-0-not-returning-proper-data-with-selec

I'm wondering if the persistent nature of modperl could lead to the following sequence:
- Autocommit is off and using InnoDB
- 1 session connects and reads data, no rollback or commit
- 1 session connects and writes data, commit
- The first session reads again, gets the same db handle for which the transaction is still ongoing and therefore retrieves cached data