Custom post type meta box empty after save

As @Milo Said. Your function is ended early. Try this for save_post action.

add_action( 'save_post', 'mob_datebox_save', 1, 2);  
function mob_datebox_save( $post, $post_id )  
{  
    // Bail if we're doing an auto save  
    if( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) return; 

    // if our nonce isn't there, or we can't verify it, bail 
    if( !isset( $_POST['meta_box_nonce'] ) || !wp_verify_nonce( $_POST['meta_box_nonce'], 'my_meta_box_nonce' ) ) return; 

    // if our current user can't edit this post, bail  
    if( !current_user_can( 'edit_post', $post_id ) ) return;  



// now we can actually save the data  
    $allowed = array(   
        'a' => array( // on allow a tags  
            'href' => array() // and those anchors can only have href attribute  
        )  
    );  

    // Make sure your data is set before trying to save it  
    if( isset( $_POST['mob_datetext'] ) )  
        update_post_meta( $post_id, 'mob_datetext', wp_kses( $_POST['mob_datetext'], $allowed ) );  

}

Also try to use <?php instead of <? for PHP opening.