WordPress: Loop - PageNavi (WordPress Forum)

<?php
    // Problema apresentado no Fórum Oficial do WordPress em http://br.forums.wordpress.org/topic/paginacao-nao-e-feita-no-index-com-o-pagenavi

    $portfolio = new WP_Query( array('category_name' => 'portfolio', 'posts_per_page' => 5, 'paged' => get_query_var('paged') ) );

    if ( $portfolio->have_posts() ) :
        while ( $portfolio->have_posts()) : $portfolio->the_post();?>
        <a href="<?php the_Permalink();?>" title="<?php the_title();?> - Paulo Mendes | Fotografia" class="a_posts">
        <div class="posts">
        <div class="posts_foto">
        <div class="titulo_img">
        <div class="titulo2">
        <?php the_title();?>
        </div>
        </div><!-- FECHA_CLASS_TÍTULO -->

        <?php if(has_post_thumbnail( )): ?>
        <?php the_post_thumbnail('featured'); ?>
        <?php else: ?>
        <img alt="<?php the_title(); ?>" src="<?php bloginfo('template_directory'); ?>/img/sem-thumbnail.jpg" />
        <?php endif; ?>

        </div><!-- FECHA_CLASS_POSTS_FOTO -->

        <span class="titulo_posts"><?php the_title();?></span>

        <?php the_excerpt(); ?>

        </div><!-- FECHA_ID_POSTS -->
        </a>
        <?php endwhile; ?>

        <div class="paginator">

        <?php wp_pagenavi( array( 'query' => $portfolio ); ?>

        </div><!--DIV_CLASS_PAGINATOR -->

    <?php else:?>
    <?php endif;?>