[Freeswitch-users] session_in_hangup_hook

Happy new year I'm trying to get spandsp fax related channel variables after hangup. I'm using session_in_hangup_hook=true in mod_managed. some times it is working (session variables are accessible) and some times not. I've read on the ML that it's just applicable in lua javas.... but why it is sometimes working,should I do any special configuration so it work always!?