A2lix Translation Form Bundle can not validate

Question

I use the A2lix Translation Form Bundle to realize database translation of entities. I create a entity page, which look like this:

class Page
{
    /**
     * Must define for translating this entity
     */
    use ORMBehaviors\Translatable\Translatable;

    /**
     * @ORM\Column(type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    protected $id;
}

I create also a "PageTranslation" entity:

class PageTranslation
{

    use ORMBehaviors\Translatable\Translation;

    /**
     * @ORM\Column(type="string", length=25)
     */
    protected $title;
}

In the form "PageType" i include the translations:

 public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder->add('translations', 'a2lix_translations', array(
                        'fields' => array(
                            'title' => array(
                                'label' => 'pageTitle',
                                'field_type' => 'text',
                                'attr' => array()
                            )
                        )
                ));
    }

    /**
     * Define mapper for this form
     * @param OptionsResolverInterface $resolver
     */
    public function setDefaultOptions(OptionsResolverInterface $resolver)
    {
        $resolver->setDefaults(array(
            'data_class' => 'App\MyBundle\Entity\Page',
            'cascade_validation' => true,
        ));
    }

I would like to validate the title attribute which is defined in the "PageTranslation" entity.

App\MyBundle\Entity\Page:
    properties:
        translations:
            - Valid: ~

App\MyBundle\Entity\PageTranslation:
    properties:
        title:
            - NotBlank: ~
            - Length:
                max: 255

But if i send the form with a empty title, the validation return as value "TRUE". Can someone give me a hint for my issue?