Content mirror posts and the_content

I created a shortcode which filters and lists some posts. Some of them are standard posts, some of them contains content mirror. When I add the shortcode to the TinyMCE Editor, all works fine.

Now I wanted to do the filtering and listing automatically without pasting my shortcode into 1000 pages (via custom fields). So i created the following function. It adds the shortcode to the_content without pasting it in the editor, it is only mentioned in PHP.

function post_filter($content)
{
   global $post;
   global $content_is_mirror;

   // Metadata/ Custom Fields
   $version = get_post_meta($post->ID, 'version', true);
   $product = get_post_meta($post->ID, 'product', true);
   $status = get_post_meta($post->ID, 'post_status', true);

   // Posts with Content Mirror Shortcode
   if (isset ( $content_is_mirror )) { return; }

   $content .= '<h1>Filter</h1>';

   $content .= do_shortcode('[posts version="' . $version . '" product="' . $product . '" post_status="' . $status . '"]');

   return $content;
}
add_filter('the_content','post_filter');

If I add this line, the page is broken (only on pages that contain posts with content mirror):

$content .= do_shortcode('[posts version="' . $version . '" product="' . $product . '" post_status="' . $status . '"]');

So i added a temporary solution (found on the FAQs of this plugin):

global $content_is_mirror;
   if (isset ( $content_is_mirror )) { return; }

Now, the site is fine, it shows all what it should.
BUT my table of contents does not appear anymore, maybe because I did a return, but nothing else seems to fix it.
If I echo the shortcode, all is fine (but without table of contents), but I really need to add it to post content, because it is important for generating a table of contents.

Now I suppose the reason is
– $content .= ...
– return $content;
– add_filter('the_content', 'post_filter');

I already did, but it does not change anything.

I just want to inform you that I found the solution. I outcommented line 167 in contentmirror.php and it now it works. My function doesn’t need $content_is_mirror anymore. Maybe the filters don’t like each other 😉

//$post_content = apply_filters('the_content', $post_content);