[ingo] mailbox path in procmail script

[hermooz at hermooz.net]

Hi all. 
I've got an instance of ingo configured to generate procmail scripts for
vacation, forward, ecc.
All works well except for generic filters rules, that apparently got the
path for the mailbox in the procmail wrong, i.e. the rule gets written like
this:

##### Rulename #####
:0
* ^From:.*AnyString
Foldername

while that should be

##### Rulename #####
:0
* ^From:.*AnyString
mail/Foldername

I tryed to open a bug but I've been told that this is a matter that should
be settled with a configurations in backends.php.
This is mine:

$backends['procmail'] = array(
    'driver' => 'vfs',
    'preferred' => 'relay.domain.com',
    'hordeauth' => true,
    'script' => 'procmail',
    'scriptparams' => array(
        // What path style does the IMAP server use ['mbox'|'maildir']?
        'path_style' => 'maildir',
        // An array of variables to append to every generated script.
        // Use if you need to set up specific environment variables.
        'variables' => array(
            'DEFAULT' => '$HOME/mail',
        )
    )
);

The script do gets written and uploaded to the server, so I guess the
driver is ok, and I focused on the scriptparams.
I've tried different configurations of 'path_style' and 'DEFAULT' values,
but to no avail. 
Anybody can help me in understanding how this works? 
Thanks very much!

Ciao,
Fabrizio