Data Enterer Metabox

gistfile1.php

<?php

class WotDataEntererListMetabox {
    
    public function __construct() {
        add_action( 'add_meta_boxes', array( &$this, 'add' ) );
        add_action( 'save_post', array( &$this, 'save' ) );
    }
    
    public function add() { 
        add_meta_box(
                'wot_data_enterer',
                'Data Enterer assignment',
                array( &$this, 'render' ),
                'tribe_events'
        );
        add_meta_box(
                'wot_data_enterer',
                'Data Enterer assignment',
                array( &$this, 'render' ),
                'tribe_venue'
        );
        add_meta_box(
                'wot_data_enterer',
                'Data Enterer assignment',
                array( &$this, 'render' ),
                'tribe_organizer'
        );
    }
    
    public function save( $PostId ) {
        // 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;
        
        if( isset( $_POST['wot_data_enterer'] ) && is_numeric( $_POST['wot_data_enterer'] )) {
             //wp_update_post( array( 'ID' => $PostId, 'post_author' ) );
            global $wpdb;
            $wpdb->update( $wpdb->posts, 
                            array( 'post_author' => $_POST['wot_data_enterer'] ),
                            array( 'ID' => $PostId )
                   );
        }
    }
    
    public function render( $Post ) {
        $s = '<select name="wot_data_enterer">';
        
        $s .= '<option style="background-color: #eaeaea">Senior Data Enterer</option>';
        foreach( $this->getSrEnterers() AS $e ) {
            $s .= '<option value="' . $e->ID . '" ' . selected( $Post->post_author, $e->ID, false) . '>' . $e->display_name . '</option>';
        }
        
        $s .= '<option style="background-color: #eaeaea">Data Enterers</option>';
        foreach( $this->getEnterers() AS $e ) {
            $s .= '<option value="' . $e->ID . '" ' . selected( $Post->post_author, $e->ID, false) . '>' . $e->display_name . '</option>';
        }
        
        $s .= '</select>';
        
        echo $s;
    }
    
    private function getSrEnterers() {
        $sr = get_users( array( 'role' => 'senior_data_enterer' ) );
        
        return $sr;
    }
    
    private function getEnterers() {
        $d = get_users( array( 'role' => 'data_enterer' ) );
        
        return $d;
    }
} // end class

The getSrEnterers() and getEnterers() methods seem to function appropriately, though I did not try changing the user list to determine if they are also being cached. Based off the other caching here though I would assume they are