On my website http://www.exaget.com/, the sub-menu is now permanently displayed. It was working ok as a pull down menu before. This was working fine before. I am not sure when exactly it got corrupted but the last plugin I added was EmbedIt, which I have since deleted.
I am not even sure where to look. I have looked within style.css and compared the navigation sections with the original and there are no differences that I can spot.
This was developed by someone else. The style.css starts off with :
Theme URI: http://wordpress.org/extend/themes/twentytwelve
Author: the WordPress team
Author URI: http://wordpress.org/
Description: The 2012 theme for WordPress is a fully responsive theme that looks great on any device. Features include a front page template with its own widgets, an optional display font, styling for post formats on both index and single views, and an optional no-sidebar page template. Make it yours with a custom menu, header image, and background.
License: GNU General Public License v2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Tags: light, gray, white, one-column, two-columns, right-sidebar, flexible-width, custom-background, custom-header, custom-menu, editor-style, featured-images, flexible-header, full-width-template, microformats, post-formats, rtl-language-support, sticky-post, theme-options, translation-ready
Text Domain: twentytwelve
This theme, like WordPress, is licensed under the GPL.
Use it to make something cool, have fun, and share what you’ve learned with others.
Similar references to Twenty Twelve are in all the other files too.
So I have always assumed it is the Twenty Twelve theme.