I don't know why the proper classes for menu item are not generated - all the elements in the tree which has subtree get only
menu-item menu-item-type-post_type. The elements, which don't have children, get proper classes after being clicked (active).
Part of the menu structure: http://imgur.com/5Lj00.png
$args = array( 'menu' => 'Main menu', 'container' => '', 'menu_id' => 'nav', ); wp_nav_menu($args);
When you visit e.g. http://lichens.ie/view-lichens-by/lichens-by-habitat/ you can see that it has no 'current' class. As well as it's parent.
PS Sorry for posting 'not working links' - it's because of reputation limitation
Any ideas - help much appreciated.