I have setup emacs so that I can run multiple versions simultaneously.

- I opened the same file (somefile.txt) simultaneously in an emacs 24.5
instance and an emacs 24.4 instance (both with -Q option)
- Did M-x global-auto-revert-mode in both.
- From terminal when I echoed some string (echo 1234 >> somefile.txt) to
that file

But only the emacs 24.4 buffer auto-reverted.

I verified that the same bug is present in the emacs master branch too
(emacs 25.0.50.2 last built on 04/24).

In GNU Emacs 24.5.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.10.4)
 of 2015-04-24 on ...
Repository revision: 866501efe0fdc0c29448e0aaf8696eb0a3c8fcd6
Windowing system distributor `The X.Org Foundation', version 11.0.60900000
System Description: Red Hat Enterprise Linux Client release 5.10 (Tikanga)

Configured using:
 `configure --prefix=/home/kmodi/usr_local/apps/emacs/emacs-24.5
 CPPFLAGS=-fgnu89-inline'

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-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

Recent messages:
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 message format-spec rfc822 mml
easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util help-fns mail-prsvr mail-utils time-date 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 71377 5779)
 (symbols 48 17554 0)
 (miscs 40 35 113)
 (strings 32 9238 5022)
 (string-bytes 1 268401)
 (vectors 16 8917)
 (vector-slots 8 383608 17837)
 (floats 8 63 81)
 (intervals 56 177 3)
 (buffers 960 11)
 (heap 1024 257035 626))