form_set_error message not displayed when using an AJAX field on a form (with a AJAX callback using commands)

Hello,

In Drupal 7's Form API, when using #AJAX to refresh fields, error messages from validation are not displayed until the entire page is refreshed. I see the field I refreshed highlighted in the error state, but the user does not see the associated message until it's too late (they've reloaded the page, or gone to another page).

Note: I'm using multi-commands with a callback (mandatory in my module to accomplish the desired behavior):

/**
* Form ajax callback
*/
function berp_product_mgr_add_new_item_ajax_callback($form, $form_state) {

$commands[] = ajax_command_replace(NULL, render($form['berp_product_mgr_item_list']));
$commands[] = ajax_command_invoke('#' . $form['berp_product_mgr_item_list']['new_item_code']['#id'], 'focus');

return array('#type' => 'ajax', '#commands' => $commands);
}

To solve my problem I have also tried to add to my commands array the following:

// Remove the old messages div, clearing existing messages.
$commands[] = ajax_command_remove('#messages');
// Append a new messages div with our latest errors and messages.
$commands[] = ajax_command_after('#header-region', '

');

But unfortunately, this is still not displaying the error message when refreshing the form with AJAX.

Any suggestion would be very appreciate to solve my problem!

Thanks in advance!

Benoit