installation / administration problem

Fresh installation of FreePBX 2.11 on a newly installed O.S.

When I tried to add backup/restore module, it produced an error, because it was trying to insert a value of '' as id field in a backup table which had autoincrement for id field.
I edited install.php, removed all the id '' lines , i.e. i did:
—
//create default servers
$server['legacy'] = array(
COMMENTED 'id' => '',
'name' => 'Legacy Backup',
'desc' => _('Location of backups pre 2.10'),
'immortal' => '',
'type' => 'local',
'path' => '_ASTVARLIBDIR_/backups',
);
—

and the installation completed succesfully, also creating the backup tenplates
When I tried to insert a new backup job, I got the same kind of error:
----------
FATAL ERROR

REPLACE INTO backup (id, name, description) VALUES ('', 'giornaliero', 'giornaliero') [nativecode=1366 ** Incorrect integer value: '' for column 'id' at row 1]

Trace Back
/srv/www/amp/admin/modules/backup/functions.inc/backup.php:180 die_freepbx()
[0]: REPLACE INTO backup (id, name, description) VALUES ('', 'giornaliero', 'giornaliero') [nativecode=1366 ** Incorrect integer value: '' for column 'id' at row 1]

/srv/www/amp/admin/modules/backup/page.backup.php:59 backup_put_backup()
[0]:

/srv/www/amp/admin/config.php:424 include()
[0]: /srv/www/amp/admin/modules/backup/page.backup.php
-----------------

So my guess now is that it was not a bug in install php, but into the function backup_put_backup(), that shoul omit to insert "id" if id value is ''.

Or maybe could it be some php module missing from my O.S. installation ?

O.S. opensuse 13.1
asterisk version 11.7.0
mysql version 5.6.12
php version 5.4.20
apache2 version 2.4.6

thanks in advance,
Andrea