I believe there's a but with the admin fly-out menus in Twenty Twelve.
I had been working in a Twenty Twelve child theme (minimal mods) on a plugin of mine and noticed the fly-out menus not working on the Dashboard page only. The menus worked on all other interior pages, it was specific to the Dashboard. So I disabled all plugins (except the beta tester) and the issue remained. Then switched to Twenty Twelve parent theme and the issue remained. Then switched to the Twenty Eleven theme and the issue went away.
Has anyone else ran into/noticed this issue?