I've done something, and I don't know what, to create another persistent link on the Admin menu, called Manage Content, only this, as the second one, is managing a particular content type "ToDo". No matter whether I delete the menu entry or rename it from the database backend, it rebuilds, and occupies the same name. There are no custom modules I have set up to alter this.
What am I looking for to diagnose this? A rogue menu_alter somewhere?