Taxonomy term archive default loop returns 1 record instead of 8

Question

I have a Custom Post Type called "book" and a custom taxonomy for this CPT called "books". One term's slug of this taxonomy is "accepting-yourself". Here's the code of the "accepting-yourself" archive page (URL: my_site/books/accepting-yourself/):

if ( have_posts() ) : 
    while ( have_posts() ) : the_post(); 
    echo get_the_title();
    endwhile;
endif;

This should return all the "book" posts in custom taxonomy "books", that's 8 posts. Instead it returns only one.

Just in case here's the code defining my custom post type and custon taxonomy:

/*------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 
CUSTOM POST TYPE : BOOK
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------*/

function my_custom_post_book() {
    $labels = array(
        'name'               => _x( 'Books', 'post type general name' ),
        'singular_name'      => _x( 'Book', 'post type singular name' ),
        'add_new'            => _x( 'Add New', 'book' ),
        'add_new_item'       => __( 'Add New Book' ),
        'edit_item'          => __( 'Edit Book' ),
        'new_item'           => __( 'New Book' ),
        'all_items'          => __( 'All Book' ),
        'view_item'          => __( 'View Book' ),
        'search_items'       => __( 'Search Book' ),
        'not_found'          => __( 'No books found' ),
        'not_found_in_trash' => __( 'No books found in the Trash' ), 
        'parent_item_colon'  => '',
        'menu_name'          => 'Books'
    );
    $args = array(
        'labels'        => $labels,
        'description'   => 'Holds our books specific data',
        'public'        => true,
        'menu_position' => 4,
        'supports'      => array( 'title', 'editor', 'thumbnail', 'excerpt', 'comments', 'custom-fields'),
        'has_archive'   => true,
    );
    register_post_type( 'book', $args );    
}
add_action( 'init', 'my_custom_post_book' );

function my_updated_messages_book( $messages ) {
    global $post, $post_ID;
    $messages['book'] = array(
        0 => '', 
        1 => sprintf( __('Book updated. <a href="%s">View book</a>'), esc_url( get_permalink($post_ID) ) ),
        2 => __('Custom field updated.'),
        3 => __('Custom field deleted.'),
        4 => __('Book updated.'),
        5 => isset($_GET['revision']) ? sprintf( __('Book restored to revision from %s'), wp_post_revision_title( (int) $_GET['revision'], false ) ) : false,
        6 => sprintf( __('Book published. <a href="%s">View book</a>'), esc_url( get_permalink($post_ID) ) ),
        7 => __('Book saved.'),
        8 => sprintf( __('Book submitted. <a target="_blank" href="%s">Preview book</a>'), esc_url( add_query_arg( 'preview', 'true', get_permalink($post_ID) ) ) ),
        9 => sprintf( __('Book scheduled for: <strong>%1$s</strong>. <a target="_blank" href="%2$s">Preview book</a>'), date_i18n( __( 'M j, Y @ G:i' ), strtotime( $post->post_date ) ), esc_url( get_permalink($post_ID) ) ),
        10 => sprintf( __('Book draft updated. <a target="_blank" href="%s">Preview book</a>'), esc_url( add_query_arg( 'preview', 'true', get_permalink($post_ID) ) ) ),
    );
    return $messages;
}
add_filter( 'post_updated_messages', 'my_updated_messages_book' );


/*------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ 
CUSTOM BOOK TAXONOMY
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------*/

$labels = array(
    'name'                          => 'Books',
    'singular_name'                 => 'Book',
    'search_items'                  => 'Search Books',
    'popular_items'                 => 'Popular Books',
    'all_items'                     => 'All Books',
    'parent_item'                   => 'Parent Book',
    'edit_item'                     => 'Edit Book',
    'update_item'                   => 'Update Book',
    'add_new_item'                  => 'Add New Book',
    'new_item_name'                 => 'New Book',
    'separate_items_with_commas'    => 'Separate Books with commas',
    'add_or_remove_items'           => 'Add or remove Books',
    'choose_from_most_used'         => 'Choose from most used Books'
    );

$args = array(
    'label'                         => 'Books',
    'labels'                        => $labels,
    'public'                        => true,
    'hierarchical'                  => true,
    'show_ui'                       => true,
    'show_in_nav_menus'             => true,
    'args'                          => array( 'orderby' => 'term_order' ),
    'rewrite'                       => array( 'slug' => 'books', 'with_front' => false ),
    'query_var'                     => true
);

register_taxonomy( 'books', 'book', $args );

Answer 1

Your code should hook the CPT registration to init, though I don't know if that is part of the issue.

Your code is relatively simple, and it works just fine for me when I test it.

Unless you've altered the main query, on the /books/accepting-yourself archive page the Loop you've posted should return:

1. The published posts
2. In your "book" CPT
3. In your "accepting-yourself" term
4. Limited to the number you've selected in "Settings -> Reading" under "Blog pages show at most"

It really sounds like item #4 is the problem. If you can verify that that is not it, then my next guess would be that something is already altering the main query and setting the posts_per_page argument to 1-- probably a poorly written callback for the pre_get_posts hook.

As mentioned, I tested your code and I do not get any unexpected behavior. Without more information, that is all I've got. If you can edit more detail into the question I'll see what else I can do.

Answer 2

The problem using the native Reading Settings is that it effects the main loop.

What you can do is use pre_get_posts with a conditional tag to control how many posts in a CPT or Taxonomy archive are displayed:

You can modify this code with the conditional for your CPT or taxonomy archive page:

add_action( 'pre_get_posts', 'wpsites_taxonomy_archive_limit' );
function wpsites_taxonomy_archive_limit( $query ) {

if( $query->is_main_query() && !is_admin() && is_tax( 'books' ) ) {
    $query->set( 'posts_per_page', '8' );
}

}

The above code displays 8 posts in the custom taxonomy type archive, book.

For a custom post type archive, use something like this:

add_action( 'pre_get_posts', 'wpsites_cpt_archive_limit' );
function wpsites_cpt_archive_limit( $query ) {

if( $query->is_main_query() && !is_admin() && is_post_type_archive( 'book' ) ) {
    $query->set( 'posts_per_page', '8' );
}

}

Source http://codex.wordpress.org/Conditional_Tags#A_Taxonomy_Page