I just installed Wordpress into my server and I am currently using the "graphene" theme to test my wordpress blog. I have two pages in addition to the front page, which is "about us" and "sample page". I noticed that if I'm using a custom menu order that is created from the "menu" section under the "Appearance" options in the dashboard, the text "this is the 'about us' page." appears under the "about us" button in the navigation menu. Removing all page text from the "about us" page didn't remove the description from the menu button.
Without custom menu, the navigation button looks like this :
With custom menu, the navigation button has description :
|this is the "about us" page.|