current_page_item class not working correctly

I’m using wp_list_pages to list the children of a page in the sidebar. The first page listed is always highlighted (has the current_page_item class). No matter which of the other sibling pages I’m on, the first is still getting the current_page_item class. I cannot figure out what’s causing this. Any ideas? I’m using 2.6.3. The pages in question can be found here.