From http://mantis.testlink.org/view.php?id=5512
IMPORTANT NOTICE
date/time in TestLink Event Viewer is managed in a completely different way that for other items.
date/time is saved used the technique used by mantis: saved in UNIX TIME format, using always UTC date/time.
When this date/time need to be presented to user on GUI, TIMEZONE configured on php.ini is used.
That's why if you do changes on date.timezone you will see that date/time will change on Events Viewer, while creation/modification date/time for test case versions remains the same.
For all other items date/time is saved to DB on a timestamp field without saving TIMEZONE used at the moment when TL get the date/time.
Probably we will need to do a big refactor on 2.0, to save always date/time on DB on UTC.