CTools API change causes warning: Following layouts have a "content" region key which is invalid

Also, if I select the parent "Zen" theme at Drupal's "Appearance", the error does not appear; only have this error if I choose the subtheme.

I have just tried the below and it makes the error goes away:

According to the Panels' document at http://drupal.org/node/495654 , point 4: about editing the *.inc files inside the "layouts" directory, there should be a "panels" array:

in the panels array we will define the regions in which content can be placed once our layout is finished, just add a new item for each area, we will end up with this:

'panels' => array(
	'top' => t('Top'),
	'left' => t('Left side'),
	'right' => t('Right side')
),

However in the "layouts" directory that come with the Zen theme, the wording "panels" was coded "regions" in the *.inc files. For example, in the zen/layouts/zen_one_sidebar_first/zen_one_sidebar_first.inc :

<?php
// Plugin definition
$plugin = array(
  'title'       => t('One sidebar before content'),
  'icon'        => 'zen-one-sidebar-first.png',
  'category'    => t('Columns: 2'),
  'theme'       => 'zen_one_sidebar_first',
  'css'         => 'zen-one-sidebar-first.css',
  'admin theme' => 'zen_one_sidebar_first_admin',
  'admin css'   => 'zen-one-sidebar-first-admin.css',
  'regions'     => array(
    'content'       => t('Content'),
    'sidebar_first' => t('Sidebar'),
  ),
);

If I change the five directories inside "layouts" from "regions" to "panels", the error disappears.

I do not know whether this is a correct way to deal with the problem. I do not know whether the "regions" is coded intentionally too.

I've just found that this problem only occurred on my old installation. That is, I added the Zen core and sub-theme to an existing site, the above mentioned error message was shown on the front page every time it loads, and also when I "drush cc all". The only way to get rid of it is to change "regions" to "panels" inside the "layouts" directory as I said above at #2.

However, if I use the same CTools, Panels, Zen core theme and sub-theme on a brand new Drupal installation, the problem did not appear.

I suspected that there are some settings which caused the problem. But since I did not defined any Panels yet, I do not know how to fix it.

If I disable the Panels module, the error message is gone. And after the Panels module is enabled again, the error message comes back.