En los posts tenes ese problema?
Sí también lo tenía, al final lo que hice fue reemplazar caracteres en la base de datos, de esta manera:
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'á', 'á');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'é', 'é');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'ó', 'ó');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'ú', 'ú');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'É', 'É');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'Ó', 'Ó');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'Ú', 'Ú');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'ñ', 'ñ');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, 'Ñ', 'Ñ');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, '¿', '¿');
UPDATE phpbb_posts SET post_text = REPLACE(post_text, '¡', '¡');