menu_set_item fails for forum paths

I am currently using an adapted version of the menutrails module for drupal 7 (http://drupal.org/node/940206#comment-4126304) and it works fine so far, but not for forum paths... The Path that should be active should be forum/3 and that is what I pass to the menu_set_item function, but it is not set active. Does the forum module overwrite things later on and how could I change it? Or is it a bug?