This problem has been resolved, adding it here if others encounter it ...
Poblem: Frequent logouts and sessions getting swapped (or hijacked) for some logged in users. When session swap / hijack happens you would see someone else's name as logged in user on top right and if you do not notice and create an issue or comment, it will go as the other user. Conversely, you may find an issue or comment created by your name but you didn't do it.
Environment: JIRA 6.0.x with Apache 2.2.15 as reverse proxy on CentOS 6.2