He usado este codigo, y me sigue leyendo el de por defecto:
<?php $comments_args = array(
'author' =>'<p class="comment-form-author"><label for="author"></label><input id="author" name="author" type="text" value="Nombre" size="30"/></p>',
'email' => '<p class="comment-form-email"><label for="email"></label><input id="email" name="email" type="text" value="e-mail" size="30"/></p>',
'label_submit' => __('Comentar'),
'comment_field' => '<p class="comment-form-comment"><textarea id="comment2" name="comment" cols="45" rows="2" aria-required="true" placeholder="Introduce tu comentario..."></textarea></p>',
);
comment_form($comments_args); ?>
Sólo me coge bien el texarea.
Alguna idea?