Okay, this has to be the weirdest drupal bug I have come to see thus far and I have to admit I didn't see this thing all the way through, partly because of it's quirkiness, partly because of a deadline I already busted.
I wrote a module which enables the site admin to create menu-blocks (completely independent from the module with that name!) that display the menu items with optional images and orders the items with some taxonomy-magic.
Now I wanted to display the main menu two times, one time as a dropdown menu like described above, and one time in the footer.
Everything works fine with that, output is just like expected. But, and this is the strange thing: If there are two blocks, the following type of error occurs for every menu-item that links to a node:
Notice: Trying to get property of non-object in node_page_title() (Zeile 2109 von /var/www/localhost/htdocs/catcruising/www/modules/node/node.module).
I've tracked this down to menu_build_tree, which I use in order to get the menu that is to be rendered.
The trace goes roughly like this: menu_build_tree -> menu_tree_check_access -> _menu_tree_check_access -> _menu_link_translate -> _menu_item_localize
As far as I can tell the following line in _menu_item_localize is the culprit:
<?php
$item['title'] = call_user_func_array($callback, menu_unserialize($item['title_arguments'], $map));
?>For some reason I cannot grasp, the second time around the node-titles are tried to be translated, calling node_page_title with the argument ($node) being a simple integer, instead of a node-object.
In case it's not yet obvious: It seems that you cannot call menu_build_tree for the same menu multiple times in the same page request.
My current workaround for this problem is setting a global variable with the menu tree, which works just fine. But I think if I tried to output the same menu once with the default drupal means and once using my module (or another) this bug would surface again.