Custom taxonomy query broken after upgrade to 4.4

Question

I just upgraded from 4.2 to 4.4 and now my taxonomy query returns empty. It has been working fine prior to the upgrade.

I have registered a custom taxonomy named 'title', which is used by my custom post type 'sg-publications'. Following the WP template hierarchy I created a template called taxonomy-title.php which uses the default query args, and up until now has correctly shown each publication by it's title.

Here is the output of $queried_object and $wp_query->request in that template:

[queried_object] => WP_Term Object
    (
        [term_id] => 1256
        [name] => Stroupe Scoop
        [slug] => stroupe-scoop
        [term_group] => 0
        [term_taxonomy_id] => 1374
        [taxonomy] => title
        [description] => 
        [parent] => 0
        [count] => 30
        [filter] => raw
    )

[queried_object_id] => 1256

[request] => 
SELECT wp_posts.* 
FROM wp_posts 
INNER JOIN wp_term_relationships 
ON (wp_posts.ID = wp_term_relationships.object_id) 
WHERE 1=1 
AND wp_posts.post_title = 'stroupe-scoop' 
AND ( 
    wp_term_relationships.term_taxonomy_id 
    IN (1374)
    ) 
AND wp_posts.post_type = 'sg-publications' 
AND (wp_posts.post_status = 'publish' 
    OR wp_posts.post_status = 'private'
    ) 
GROUP BY wp_posts.ID 
ORDER BY wp_posts.post_date 
DESC 

The problem I see in the above query is right after WHERE 1=1, for some reason it is searching for post_title = 'stroupe-scoop'. This is not correct - that is the taxonomy term slug, not the title of the post. In fact, when I comment out that line and run it against the database I get the proper returns. So what is causing WP to add that condition, when (I assume) it was not adding it before I upgraded to 4.4?

Here is taxonomy-title.php:

<?php
/**
 * @package WordPress
 * @subpackage Chocolate
 */
  global $wp_query;

  $quer_object = get_queried_object();
  $tax_desc    = $quer_object->description;
  $tax_name    = $quer_object->name;
  $tax_slug    = $quer_object->slug;

get_header();
get_sidebar();

$title = get_the_title( $ID );
$args  = array(
    'menu'            => 'new-publications',
    'container'       => 'div',
    'container_id'    => $tax_slug . '-menu',
    'menu_class'      => 'menu-top-style nav nav-tab',
    'menu_id'         => '',
    'echo'            => true,
    'fallback_cb'     => false,
    'before'          => '',
    'after'           => '',
    'link_before'     => '<i class="fa fa-chevron-circle-right fa-fw fa-2x"></i>',
    'link_after'      => '',
    'items_wrap'      => '<ul id="%1$s" class="%2$s">%3$s</ul>',
    'depth'           => 0,
    'walker'          => ''
);

?>

<div id="page-title">
  <h1><?php _e( 'Publications - ' . $tax_name, LANGUAGE_ZONE ); ?></h1>
  <p><?php _e( 'View our monthly newsletter and stay informed on the latest real estate news.', LANGUAGE_ZONE ); ?></p>

<?php wp_nav_menu($args); ?>

</div>

<div id="multicol">

<?php
if ( have_posts() ) : while ( have_posts() ) : the_post();

get_template_part( 'loop' , 'title' );

endwhile;
endif;
?>

</div><!-- end #multicol -->
<section class="page-text well"><?php _e( $tax_desc, LANGUAGE_ZONE ); ?></section>

<?php
get_footer();

And in functions.php I have this query filter:

// use pre_get_posts to remove pagination from publications
function gd_publications_pagination( $query ) {
  if ( is_admin() || ! $query->is_main_query() )
    return;

  if ( is_tax('title') ) {
    // Display all posts for the taxonomy called 'title'
    $query->set( 'posts_per_page', -1 );
    return;
  }
}
add_action( 'pre_get_posts', 'gd_publications_pagination', 1 );

Answer 1

I wouldn't recommend using a taxonomy slug that coincides with the public query variables, like title.

The title query variable was introduced in 4.4 so I think that could explain your problems.

Check out this part of the WP_Query class:

    if ( '' !== $q['title'] ) {
        $where .= $wpdb->prepare( 
            " AND $wpdb->posts.post_title = %s", 
            stripslashes( $q['title'] ) 
        );
    }

So when we use for example:

example.tld/?title=test

what should WordPress do here? Is it a taxonomy query or title search?

So I would recommend prefixing the custom taxonomy slug, e.g.

gary_title

to avoid possible name collisions.

Update:

Thanks to @ocean90 for pointing out that this is a bug, that will be fixed in 4.4.1