bug#21718: 24.5; Backgrounding emacsclient hangs emacs

[Ed Avis <eda@waniasset.com>]

I am running emacs from a text ssh session.

% emacs -Q
M-x server-start RET
M-x shell RET
% touch foo
% emacsclient foo
C-x b RET                  (switch back to shell buffer)
M-x comint-stop-subjob RET

I expected this to background the emacsclient process within the shell
window.  But it causes all of emacs to disappear from the screen, back
to the original shell prompt that launched emacs, where the emacs
process appears to have hung and can only be killed with C-c.



In GNU Emacs 24.5.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.16.6)
 of 2015-09-14 on buildvm-10.phx2.fedoraproject.org
Configured using:
 `configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
 --with-gpm=no build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
 -m64 -mtune=generic' LDFLAGS=-Wl,-z,relro'

Important settings:
  value of $LC_COLLATE: C
  value of $LC_CTYPE: en_GB.UTF-8
  value of $LC_MESSAGES: en_GB.UTF-8
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  show-paren-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Loading /usr/share/emacs/site-lisp/site-start.d/puppet-mode-init.el (source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/rpmdev-init.el (source)...done
Loading compile...done
Loading /home/eda/lib/emacs/csharp-mode-0.8.5.el
lib/emacs/csharp-mode-0.8.5.el: `flet' is an obsolete macro (as of 24.3); use either `cl-flet' or `cl-letf'. [2 times]
lib/emacs/csharp-mode-0.8.5.el: (lambda (item) ...) quoted with ' rather than with #'
Done loading /home/eda/lib/emacs/csharp-mode-0.8.5.el
Loading log-edit...done
Loading term/xterm...done
For information about GNU Emacs and the GNU system, type C-h C-a.

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug sendmail xterm time-date paren
log-edit easy-mmode message format-spec rfc822 mml mml-sec mm-decode
mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mailabbrev mail-utils gmm-utils mailheader pcvs-util
add-log warnings server csharp-mode advice help-fns byte-opt bytecomp
byte-compile cl-extra cconv cc-langs cc-mode cc-fonts easymenu cc-guess
cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs zoom-frm
frame-cmds frame-fns cl-macs avoid cl gv cl-loaddefs cl-lib compile
shell pcomplete comint ring ansi-color tooltip electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd
fontset image regexp-opt fringe tabulated-list newcomment lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 139426 4026)
 (symbols 48 22703 0)
 (miscs 40 90 93)
 (strings 32 24674 4900)
 (string-bytes 1 863595)
 (vectors 16 12515)
 (vector-slots 8 394759 2869)
 (floats 8 80 207)
 (intervals 56 226 0)
 (buffers 960 14)
 (heap 1024 40722 843))

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