date_popup default value not translated

Hello,

I have added a date_popup field in a form :

$format = 'j M Y - H:i';

$form['contact_date'] = array(
    '#type' => 'date_popup',
    '#date_format' => $format,
    '#default_value' => 'now',
    '#date_timezone' => 'Europe/Paris',
    '#date_year_range' => '0:+2',
    '#date_label_position' => 'above',
    '#title' => t('Quand souhaitez-vous être appelé ?'),
    '#date_increment' => 5,
    '#required' => FALSE,
    '#weight' => 1,
  );

The site defaut language is French.
When the field is displayed first, the month is not translated (21 apr 2010).
If the user selects a date with the date picker, the month is translated OK (21 avr 2010).
How can I get the default value translated when the form is displayed first ?

Thank you,
Frederic