Just made a dummy design with only a pagelayout.tpl on http://www.cmandev.com/
So the only code I'm using in the pagelayout is the code posted above. I changed to $primary_menu_root_node_id to the real ID but it still doesn't work :S
Nope, not running cluster mode. Just a single install on one server with MySQL on it. When I do a manual "Clear Content Cache" in the admin panel it works ofcourse. But not automatically...