Remove the current menu parent class from the Blog menu item when on the bbPress forum page

functions.php

function generate_remove_bbpress_parent_classes($class)
{
	return ( $class == 'current_page_parent' ) ? FALSE : TRUE;
}

add_filter( 'nav_menu_css_class', 'generate_remove_bbpress_parent_class' );
function generate_remove_bbpress_parent_class( $classes )
{
	switch (get_post_type())
	{
		case 'forum':
			// we're viewing a custom post type, so remove the 'current_page_parent' from all menu items.
			$classes = array_filter($classes, "generate_remove_bbpress_parent_classes");
		break;
		
		case 'topic':
			// we're viewing a custom post type, so remove the 'current_page_parent' from all menu items.
			$classes = array_filter($classes, "generate_remove_bbpress_parent_classes");
		break;
	}
	return $classes;
}