bug#17874: 24.3.92; Incorrectly isolated ع in علی

[penthief]

The following should display differently, as in 24.3.1.
A.  ع ل ی - these are the "isolated" types.
B.  علی  - this is a final, medial and initial type.
C.  عل ی‎ - the isolated ی should be joined when the space is removed. 
This is the bug demonstrated.

0. Start emacs: $ emacs -Q
1. Output علی with a bold face in the appropriate font:
(progn
  (setq buffer-face-mode-face '(:family  "DejaVu Sans Mono" 
:alternate-families  "Monaco" :height 100))
  (buffer-face-mode)
  (buffer-face-set 'bold)
  (newline)
  (insert " علی"))

 علی

2. Change to a regular face:
(buffer-face-set 'default)
 علی

What happens is ی (ARABIC LETTER FARSI YEH) switches from the final to 
the isolated type.
This is incorrect since there should be no difference in the 
representation when eval-ing the following:

(buffer-face-toggle 'bold)

The output of describe-char on the emboldened and regular differs on the 
following:

Regular (incorrect):

Composed using this font:
  
xft:-unknown-KacstDecorative-normal-normal-normal-*-11-*-*-*-*-0-iso10646-1
by these glyphs:
  [0 0 0 107 5 0 6 5 2 nil]

Bold (correct):

Composed using this font:
  xft:-unknown-KacstOne-bold-normal-normal-*-11-*-*-*-*-0-iso10646-1
by these glyphs:
  [2 2 0 200 7 0 8 2 4 nil]

Please note that this bug does not exist on 24.3.1, and I apologise if 
it is a problem with my compilation settings.

Regards,
Matt


In GNU Emacs 24.3.92.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2014-06-28 on zz
Repository revision: 117323 
schwab@linux-m68k.org-20140628072401-95qhsfaufm9fxrj8
Windowing system distributor `The X.Org Foundation', version 
11.0.11501000
System Description:     Ubuntu 14.04 LTS

Configured using:
 `configure --with-dbus --with-libotf --with-m17n-flt'

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  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
  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 input:
M-x r e p o <tab> - e - b <tab> <return>

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

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
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 help-mode easymenu 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
gfilenotify dynamic-setting system-font-setting font-render-setting
move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 72971 7323)
 (symbols 48 17511 0)
 (miscs 40 61 164)
 (strings 32 9378 3890)
 (string-bytes 1 256561)
 (vectors 16 9668)
 (vector-slots 8 389112 14907)
 (floats 8 63 385)
 (intervals 56 182 0)
 (buffers 960 12)
 (heap 1024 46452 877))