Saving data to %session with Apache::Session::File

Hi

I'm using Apache::Session::File for session management. I have a hash in 
$session{'config'} that saves some config values.

I have a script that should change these config values:

foreach ( sort keys %newconfig ) {
     $session{'config'}{$_} = $newconfig{$_};
}

this works perfectly for the script. However, the values are not written 
to the session file. Thus they are not stored permanently and if I 
reload the script, the old values are in $session again. Does anyone 
know, what might be the reason for that?

Greetings
Fabian Gut