[turba] VFS problem during import CSV address book

[Marco]

Good morning,
I have horde/turba over mysql VFS.

My trouble concerns VFS. In config/conf.php I have:

$conf['vfs']['params']['driverconfig'] = 'horde';
$conf['vfs']['type'] = 'sql';

Also in Turba I set turba/config/conf.php with:

$conf['documents']['type'] = 'horde';

In this way Turba should use Horde VFS, I suppose. But this doesn't happen.
When I try to import a CSV address book file from Import/Export link I  
see that the file has uploaded in the local file system, not in VFS.

Even if in turba/config/conf.php I set

$conf['documents']['params']['driverconfig'] = 'horde';
$conf['documents']['type'] = 'sql';

the VFS is not used. All uploaded files through import/export  
procedure are stored to the local file system.

Does anyone experience this trouble? Could you help me setting VFS for  
import CSV files in personal address book?

I don't see errors in horde log or httpd logs.
Versions are Horde 3.3.4 - Turba 2.3.1

Thank you very much
Regards
Marco