I have discovered that the category list page has the $postID the last (first, depends on :D) post on the page. It leads a false warning when the first - or last - post of the page is marked to warn.
I have modified the main.php:
if((is_admin() || is_feed() || is_login_page() || current_user_can('manage_options')) && is_single($postID))
So the warning is only displayed on single post pages. Please consider to apply this change.
Ps.: maybe the '&& is_single()' without $postID would suffice but I don't know neither php nor the WordPress.