Multiselect Array Form Validation Problem

[eluser]Unknown[/eluser]
Hello,

I'm trying to validate a multiselect array post with form validation class. But after validation, I have only the last item of the returning array...

I'm using Codeigniter 2.0.1...

construction of the form in viewer :

Code:

$skills = array('name' => 'skills[]', 'id' => 'skills', 'value' => ... 'options' => ...);
echo form_multiselect($skills['name'], $skills['options'], $skills['value']);

validation in controller :

Code:

$val = $this->form_validation;
$val->set_rules('skills[]', 'Skills', 'required');
$data['skills'] = $val->set_value('skills[]');

checking values :

Code:

print_r ($data['skills']) // returns :

6

// However, I'm waiting for an array as in $_POST.

print_r($_POST); // returns :

Array
(
    ...
    [skills] => Array
        (
            [0] => 4
            [1] => 6
        )
)

Where am I wrong ?