hook_page_alter and trying to change the '#theme_wrappers' property I'm going a bit Drupal crazy trying to change the '#theme_wrappers' property of certain blocks in my sidebar region. I am able to set it using hook_page_alter and can dpm() it and confirm it is being set, but it never calls the function I point it to:

 $element = $vars['page']['sidebar_first'];

  foreach($element as &amp;$elements){
    if (array_key_exists('#block', $elements)){
      $menuBlock = (array) $elements['#block'];
      if ($menuBlock['delta'] == "navigation" || $menuBlock['module'] == "menu"){
        $elements['#theme_wrappers'] = array('wet4_menu_tree__menu_sidebar');
      }
    }
  }

=====================

function wet4_menu_tree__menu_sidebar(&amp;$variables) {
  dpm($variables);
    return '&lt;ul class="list-group menu list-unstyled"&gt;' . $variables['tree'] . '&lt;/ul&gt;';
}


Any ideas?
As I commented above, the issue was that I was missing the &amp; before $vars in this line:

$element = $vars['page']['sidebar_first'];


It was not creating a reference so it wasn't actually setting my '#theme_wrappers' property.