Fix Blog Tab Classes on Custom Post Type Pages

gistfile1.php

<?php
// FIX BLOG TAB CLASSSES ON CUSTOM POST TYPES
function fix_blog_tab_on_cpt( $classes, $item, $args ) {
    if( !is_singular( 'post' ) && !is_category() && !is_tag() ) {
        $blog_page_id = intval( get_option( 'page_for_posts' ) );
        if( $blog_page_id != 0 ) {
            if( $item->object_id == $blog_page_id ) {
				unset( $classes[ array_search( 'current_page_parent', $classes ) ] );
			}
        }
    }
    return $classes;
}
add_filter('nav_menu_css_class','fix_blog_tab_on_cpt',10,3);