bug#25113: 25.1.90; Stale menu items after switching to a different major mode (or visiting a buffer)

[Dmitry Gutov <dgutov@yandex.ru>]

1. Start 'emacs -Q', and

- In *scratch*, M-x ruby-mode (or python-mode, or probably many others)

OR

- C-x C-f, visit a Ruby file (or, again, probably any other file)

2. See the "Lisp Interaction" menu disappear, and "Ruby" manu appear.

However, the contents of that menu are exactly the same as what was in
"Lisp Interaction".

If I toggle menu-bar-mode off and on, the menu obtains the correct
contents.

I'm also seeing a problem the menu added by a minor mode which appears
blank at first (which is fixed the same way), but let's tackle the more
obvious problem first.

Looking at older versions, the problem is present as far back as 24.3
(with python-mode; ruby-mode didn't have a menu then).

So this is probably caused by a library change, like the GTK version I
have installed.

***

In GNU Emacs 25.1.90.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
  of 2016-12-04 built on zappa
Repository revision: a3487a8121e408ee07fe019270b3bdeaac0ee960
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:	Ubuntu 16.04.1 LTS

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11