Hi,
I recently upgraded my 3.0.3 intsallation to 3.1+.
When I'm at the homepage, my navigation menu (site admin) works fine. When I'm anywhere else, where a menu item is already expanded, it seems like trying to expand another item is impossible. It flips the small arrow beside the item, but the submenu doesn't show up, or sometimes another unrelated submenu opens.
I tried switching my theme to the base one, to see if recent changes in my theme could cause the issue, but it's still happening in the base theme!
Running on IIS 7 with PHP 5.6.22.