surfhost

Solved it after way too many hours, with the following CSS:

.menu .current_page_item a, .menu .current_page_item a:visited {
	font-weight:bold;
}

.menu .page_item ul li a, .menu .page_item ul li a:visited {
	font-weight:normal;
}

.menu .page_item .current_page_item a, .menu .page_item .current_page_item a:visited {
	font-weight:bold;
}

A current_page_item is bold and all other page_item(s) are normal.