Tim Gieseking

Here is the solution I am using for this problem. This is somewhat of a hack, but it’s getting the job done. You would place this code in your functions.php.

function remove_parent($var)
{
	// check for current page values, return false if they exist.
	if ($var == 'current_page_parent' || $var == 'current-menu-item' || $var == 'current-page-ancestor') { return false; }

	return true;
}

function tg_add_class_to_menu($classes)
{
	// team is my custom post type
	if (is_singular('team'))
	{
		// we're viewing a custom post type, so remove the 'current-page' from all menu items.
		$classes = array_filter($classes, "remove_parent");

		// add the current page class to a specific menu item.
		if (in_array('menu-item-239', $classes)) $classes[] = 'current-page-ancestor';
	}

	return $classes;
}

if (!is_admin()) { add_filter('nav_menu_css_class', 'tg_add_class_to_menu'); }

One downside: I’m using an ID to decide which menu item to add the current class to, so if you delete/readd a page you have to edit this code.