This is caused by setting all of the links to "#" and selecting the "Top level of Currant Page" option in the Select in Menu section on the Currant tab.
Since all of the links are the same, all of the top level menu items are the "Currant Page", since they are all the "Currant page" They are all given the hover state.
If you set each of the top level buttons to go to a different page, you will no longer have this problem.