<?php
function my_custom_post_type_nav_classes( $classes, $item ) {
$custom_post_type = 'custom-post-type';
    if( ( is_post_type_archive( $custom_post_type) || is_singular( $custom_post_type ) )
    && get_post_meta( $item->ID, '_menu_item_object_id', true ) == get_option( 'page_for_posts' ) ){
        $classes = array_diff( $classes, array( 'current_page_parent' ) );
    }
    return $classes;
}
add_filter( 'nav_menu_css_class', 'my_custom_post_type_nav_classes', 10, 2 );