It seems this behavior at one time was intentional, but I (along with
the designers) think it looks ugly having the menu having its insides
shrinking and shifting around while fading out of existence.
There's two cases where we currently explicitly try to animate the
submenu closed -- when an item is clicked inside the submenu, and
when the toplevel closes. This removes both of those.
The user expectation is that submenus will be closed the next time the
toplevel is open even if they were open before, so force submenus closed
when the toplevel finishes fading out, without any animation.
https://bugzilla.gnome.org/show_bug.cgi?id=702539
2aae272d86