N-am intampinat niciodata probleme cu metatitle si folosesc acest plugin de la inceput; daca nu ai doar <title><? php wp_title(); ?></title> in header-ul temei ar trebui bifat si "Title settings --> Force rewrite titles".
WP No Category Base nu mai e necesar cu WP SEO care are "Setări permalink --> Strip the category base (usually /category/) from the category URL".