Description bei Exposed Filter will not show?

Hello,

with hook_form_alter i set a Description in Exposed Filter.

if ($form['#id'] == 'my-views-exposed-form') {
$form['#description'] = t('My description');
}

With Devel i see the Discription in $form['#description'] but it will not show in Form on my site.

What i make wrong?

Sorry for my bad english - i hope you understand my problem.

Thank you and Regards
Matthias