Created custom post type but selected template not staying selected

The page template for custom post type is not saved because it is checking whether the post type is “page” – it is not implemented for custom post types yet. The drop-down for the page templates was completely removed in 3.1.

This is my way how to deal with it:

/* Define the custom box */

// WP 3.0+
add_action('add_meta_boxes', 'custom_template_add_custom_box');

// backwards compatible
//add_action('admin_init', 'custom_templatet_add_custom_box', 1);

/* Do something with the data entered */
add_action('save_post', 'custom_template_save_postdata');

/* Adds a box to the main column on the Post and Page edit screens */
function custom_template_add_custom_box() {
    add_meta_box( 'custom-post-type-template', 'Custom Post Type Template', 'custom_template_inner_box', 'foo_resources', 'side' );
}

/* Prints the box content */
function custom_template_inner_box( $post ) {

    // Use nonce for verification
    wp_nonce_field( plugin_basename(__FILE__), 'custom_template_noncename' );

    if ( 0 != count( get_page_templates() ) ) {
        $page_template = get_post_meta($post->ID, '_wp_page_template', TRUE); ?>
    <p><strong><?php _e('Template') ?></strong></p>
    <label class="screen-reader-text" for="page_template"><?php _e('Page Template') ?></label><select name="page_template" id="page_template">
    <option value="default"><?php _e('Default Template'); ?></option>
    <?php page_template_dropdown($page_template); ?>
    </select>
<?php }
}

/* When the post is saved, saves our custom data */
function custom_template_save_postdata( $post_id ) {

     // verify this came from the our screen and with proper authorization,
     // because save_post can be triggered at other times

     if ( !isset( $_POST['custom_template_noncename'] ) || !wp_verify_nonce( $_POST['custom_template_noncename'], plugin_basename(__FILE__) ) )
         return $post_id;

     // verify if this is an auto save routine. 
     // If it is our form has not been submitted, so we dont want to do anything
     if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE ) 
         return $post_id;


     // Check permissions
     if ( 'page' == $_POST['post_type'] ) 
     {
       if ( !current_user_can( 'edit_page', $post_id ) )
           return $post_id;
     }
     else
     {
       if ( !current_user_can( 'edit_post', $post_id ) )
           return $post_id;
     }

     // OK, we're authenticated: we need to find and save the data

     $page_template = $_POST['page_template'];

    if ( !empty($page_template) && 'foo_resources' == get_post_type($post_id) ) {
        $page_templates = get_page_templates();
        if ( 'default' != $page_template && !in_array($page_template, $page_templates) ) {
            if ( $wp_error )
                return new WP_Error('invalid_page_template', __('The page template is invalid.'));
            else
                return 0;
        }
        update_post_meta($post_id, '_wp_page_template',  $page_template);
    }
}

/* Custom template redirection hook */

function custom_template_redirect() {
    global $post;

    if ( is_single() && 'foo_resources' == get_post_type($post) ) {
        $page_template = get_page_template();
        include($page_template);
        exit;
    }
}
add_action("template_redirect", 'custom_template_redirect');

Maybe you should consider to use Post Formats as another option.