Pagination error in custom taxonomy template - php

Question

I created a custom post type called "library", with its "documentation" taxonomy; The problem occurs in the pagination of the taxonomy template (taxonomy-documentation.php).
I have determined a number of "18" posts per page, for the number of posts there should be "7" pages, but I list "16" pages, the pages from "8" to "16" are empty.
The url of archive for the taxonomy is: Documentation Archive
The template loop is as follows:
<?php
$term = $wp_query->queried_object;
$getterm = $term->slug; // get current slug (E.g. winter2015)
$args = (array(
'post_type' => 'library',
'showposts' => 18,
'paged'=>$paged,
'tax_query' => array(
array(
'taxonomy' => 'documentation',
'field' => 'slug',
'terms' => $getterm
),
),
) );
$query = new wp_query( $args );
if ( $query -> have_posts() ) : while ( $query -> have_posts() ) : $query -> the_post(); ?>
<?php setPostViews(get_the_ID()); ?>
<div class="col-md-2">
<?php if ( get_post_meta( get_the_ID(), 'download_image', true ) ) : ?>
<a href="<?php the_permalink(); ?>" rel="bookmark" title="<?php get_the_title(); ?>">
<?php
$postID = $post->ID;
$imageURI = get_post_meta($postID, 'download_image', true);
$attachmentID = pn_get_attachment_id_from_url ($imageURI);
$imagearray = wp_get_attachment_image_src( $attachmentID, 'full');
$imageURI = $imagearray[0];
$thumbarray = wp_get_attachment_image_src( $attachmentID, 'library-thumbnail');
$thumb_imageURI = $thumbarray[0];
echo "<img class='document-thumbnail' src='". $thumb_imageURI . "' alt='". get_the_title() ."' />";
?>
</a>
<?php endif; ?>
<a class="document-title" href="<?php the_permalink() ?>" rel="bookmark" title="Permanent Link to <?php the_title_attribute(); ?>"><?php echo mb_strimwidth(get_the_title(), 0, 40, '...'); ?></a><br />
<span><?php echo __('Published by', 'cyberdocentes'); ?> <a class="author-link" href="<?php echo get_author_posts_url( get_the_author_meta( 'ID' ), get_the_author_meta( 'user_nicename' ) ); ?>"><?php the_author(); ?></a></span>
</div>
<?php endwhile; rewind_posts(); ?>
<div class="clear"></div>
<div id="pagination">
<?php include(TEMPLATEPATH . '/pagenavi.php'); if (function_exists('wp_pagenavi')) { wp_pagenavi(); } else { ?>
<div class="navigation">
<div class="alignleft">
<?php next_posts_link(__('Next posts','cyberdocentes')); ?>
</div>
<div class="alignright">
<?php previous_posts_link(__('Previous posts','cyberdocentes')); ?>
</div>
</div>
<?php } ?>
</div>
<div class="clear"></div>
<?php else : ?>
<?php endif; ?>
<?php flush(); ?>

Answer 1

Solved code:
<div class="documents-list">
<?php
$term = get_term_by( 'slug', get_query_var( 'term' ), get_query_var( 'documentation' ) );
global $wp_query;
query_posts( array_merge( $wp_query->query, array( 'posts_per_page' => 18 ) ) );
if (have_posts()) : while ( have_posts() ) : the_post(); ?>
//CODE OF THE ARTICLES HERE
<?php endwhile; rewind_posts(); ?>
<?php endif; ?>
<div class="clear"></div>
<div id="pagination">
<?php include(TEMPLATEPATH . '/pagenavi.php'); if (function_exists('wp_pagenavi')) { wp_pagenavi(); } else { ?>
<div class="navigation">
<div class="alignleft">
<?php next_posts_link(__('Next posts','cyberdocentes')); ?>
</div>
<div class="alignright">
<?php previous_posts_link(__('Previous posts','cyberdocentes')); ?>
</div>
</div>
<?php } ?>
</div>
<div class="clear"></div>
<?php flush(); ?>
</div>