magento - Magento 1.7 : Admin - Custom Customer Grid attribute - not filterable

Question

I'm not sure why, but I can't filter my attribute (it works fine with defaults ones).

Here is my code :

Config.xml

<global>
    <blocks>
        <adminhtml>
            <rewrite>
                <customer_grid>SaponeWebConcept_PrivateSells_Adminhtml_Block_Customer_Grid</customer_grid>
            </rewrite>
        </adminhtml>
    </blocks>
</global>

Grid.php

public function setCollection($collection)
{
    $collection->addAttributeToSelect('wants_to_be_vip');                    
    parent::setCollection($collection);
}

protected function _prepareColumns()
{
    parent::_prepareColumns();
    $attributeCollection = Mage::getResourceModel('eav/entity_attribute_collection')
    ->setCodeFilter('wants_to_be_vip')
    ->getFirstItem();
    $itemsOptions = $attributeCollection->getSource()->getAllOptions(false);
    $optionsArr = array();
    foreach ($itemsOptions as $option) {
        $optionsArr[$option['value']] = $option['label'];
    }

    $this->addColumn('V.I.P', array(
        'header'=> Mage::helper('customer')->__('Veut devenir V.I.P'),
        'index' => 'wants_to_be_vip',
        'type'  => 'options',
        'options' => $optionsArr,
    ));
    $this->addColumnsOrder('customer_id','wants_to_be_vip');
}

Thanks for you help !

Edit : It may need some more infos : - Values display ok. - My select box is ok too. - When I press the filter button, it loads, and nothing changes.