My blog's primary menu consists of the groups, displayed through the wordpress_list_groups function.

Basically click among the groups, the present category is outlined within the category menu, and also the listing of articles within that category are listed. Things are fine.

But when then i click one article, the course menu doesn't show the present category any longer. Anybody knows the way i could fix that?

This is actually the code i personally use to create recption menus within the sidebar.

<?php
wp_list_categories('child_of=55&sort_column=menu_order&sort_order=asc&title_li=');
?>

I discovered a good hack around the wordpress forum. It'll only show one "current" category but it is enough for me.

<?php
    if  (!is_page() && !is_home() && !is_single()){
    $catsy = get_the_category();
    $myCat = $catsy->cat_ID;
    $currentcategory = '&current_category='.$myCat;
}

    elseif (is_single()){
    $catsy = get_the_category();
    $myCat = $catsy[0]->cat_ID;
    $currentcategory = '&current_category='.$myCat;
}

    wp_list_categories('depth=1&title_li=&orderby=id&exclude=1,5,6,19,20,21,22&hide_empty=0'.$currentcategory);
    ?>

If perhaps highlighting 1 category if you have a multi-category-per-publish system, you might like to use this plugin rather (give a .used-cat class inside your stylesheet, alongside the .current-cat class supplied by wordpress).

'parent' is not a legitimate argument for wordpress_list_groups.

Also, are you certain exactly the same code is supplying the course list for the category page and also the publish page? The code may be inside an is_category or perhaps is_publish/is_page block.