Zend FR

$UserForm = new Model_Form_User();
Zend_Debug::dump($UserForm->getValues());

/*
array(2) {
  ["colors"] => string(1) "R" // récupère toujours cette valeur
  ["submit"] => NULL
}
*/

Zend_Debug::dump($_POST);

/*
array(2) {
  ["colors"] => string(1) "G" // récupère la bonne valeur
  ["submit"] => string(7) "Valider"
}
*/


// le modèle

public function init()
{
     $this->setAttrib('enctype', 'multipart/form-data');
     $options = array('R' => 'red', 'G' => 'green', 'B' => 'blue');
     $colors = new Zend_Form_Element_Radio('colors');
     $colors->setRequired(true)
               ->setValue('R')
               ->setOptions(array('separator' => ''))
               ->setMultiOptions($options );
     $this->addElement($colors);

     $submit = new Zend_Form_Element_Submit('submit');
     $submit->setLabel('Valider');
     $this->addElement($submit);
}