In
http://tracker.in-portal.org/view.php?id=1340 task (in 5.2.0) we've made change due which session isn't stored to database (session methods are still available in code).
After further testing in 5.2.1-B1 we've discovered, that session-related cookies (sid, cookies_on, etc.) are still sent.
This can be detected only, when /tools/cron.php is executed from PHP CLI and "Cannot modify header information - headers already sent by ..." warning is raised.