Session Path Again

My standard session.save_path in php.ini ist /tmp which is fine.
I tried to run two versions of FA in the same broser - didn't work and therefore I tried to separate the session paths by adding this to session.inc as suggested elsewhere:

$session_save_path = dirname(__FILE__).'/../tmp2';

The directory exists and has exactly the same owner/permission level as /tmp.
Fact is that my session files irrespective of the setting in session.inc get stored in /tmp.
I also tried to set the path in .htaccess but the system logged me out immediately.

I could run two versions in the same browser before but that apparently changed.
Any ideas?

rgds
rl