bug#26104: 26.0.50; In Ubuntu, having mouse over other frame cause Alt key to produce a <switch-frame> event

[Jonathan Ganc]

In Ubuntu, if I have two frames open and the mouse is positioned over 
the other frame (i.e. not over the active one), pressing the Alt key 
produces a <switch-frame> event.

While this event does nothing in itself, it disrupts things like 
yank-pop, which no longer works if it is bound to M-y as usual (because 
instead of the command sequence yank -> yank-pop, we now have yank -> 
handle-switch-frame -> yank-pop, which gives an error "user-error: 
Previous command was not a yank").

To be honest, I don't know enough about X-Windows to know if this is 
emacs' fault or x-windows fault. But it's very annoying.

[Tried on Emacs versions 24.5, 25.1, and the 26.0 and Ubuntu 16.10.]


In GNU Emacs 26.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.20.9)
 of 2017-03-13 built on lgw01-17
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:    Ubuntu 16.10

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured using:
 'configure --build=x86_64-linux-gnu --prefix=/usr
 '--includedir=${prefix}/include' '--mandir=${prefix}/share/man'
 '--infodir=${prefix}/share/info' --sysconfdir=/etc --localstatedir=/var
 --disable-silent-rules '--libdir=${prefix}/lib/x86_64-linux-gnu'
 '--libexecdir=${prefix}/lib/x86_64-linux-gnu' --disable-maintainer-mode
 --disable-dependency-tracking --prefix=/usr --sharedstatedir=/var/lib
 --program-suffix=-snapshot --with-modules=yes --with-x=yes
 --with-x-toolkit=gtk3 --with-xwidgets=yes 'CFLAGS=-g -O2
 
-fdebug-prefix-map=/build/emacs-snapshot-5_17hP/emacs-snapshot-93215-94b59f7-emacs=.
 -fstack-protector-strong
 -Wformat -Werror=format-security' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

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

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
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prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
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Memory information:
((conses 16 96862 6611)
 (symbols 48 20194 1)
 (miscs 40 47 82)
 (strings 32 17628 4506)
 (string-bytes 1 566213)
 (vectors 16 14655)
 (vector-slots 8 483106 4490)
 (floats 8 48 68)
 (intervals 56 290 0)
 (buffers 976 12))