Bug#439767: libpango1.0-0: pango renders U+200B (zero width space) visibly under certain conditions

[Rich Felker]

Package: libpango1.0-0
Version: 1.16.5-1
Severity: normal

After upgrading my system, the latest Pango renders U+200B (zero-width
space) visibly under certain conditions, as a "missing glyph" box
containing the hex value. Particularly, Pango seems to be a looking
for a glyph for this character matching the current language/script.
In my case, Tibetan characters adjacent to U+200B cause the
misrendering to happen.

I first observed the problem on a Google search (in Iceweasel) but
have since been able to reproduce it in GTK+ text widgets by first
typing U+200B (using an input method) then moving the cursor before
the U+200B character and typing any Tibetan character. Thus, I am
fairly confident that the bug is in Pango itself and not GTK+ or
Iceweasel.

I suspect the Tibetan fonts I am using lack a glyph for U+200B, but
Pango should not be insisting on trying to find a "Tibetan version" of
this character. It probably shouldn't even look for glyphs at all, but
instead always treat it as a zero-width character with no visible
glyph... but if it is going to use a glyph it should grab one from any
available font.

Screenshot of the issue:
http://www.aerifal.cx/~dalias/images/200b.png

-- System Information:
Debian Release: lenny/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: i386 (i686)

Kernel: Linux 2.6.21-rc5-nkl1
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/bash

Versions of packages libpango1.0-0 depends on:
ii  libc6                   2.6.1-1          GNU C Library: Shared libraries
ii  libcairo2               1.4.10-1         The Cairo 2D vector graphics libra
ii  libdatrie0              0.1.1-4          Double-array trie library
ii  libfontconfig1          2.4.2-1.2        generic font configuration library
ii  libfreetype6            2.3.5-1+b1       FreeType 2 font engine, shared lib
ii  libglib2.0-0            2.14.0-2         The GLib library of C routines
ii  libpango1.0-common      1.16.5-1         Modules and configuration files fo
ii  libthai0                0.1.8-3          Thai language support library
ii  libx11-6                2:1.0.3-7        X11 client-side library
ii  libxft2                 2.1.12-2         FreeType-based font drawing librar
ii  libxrender1             1:0.9.2-1        X Rendering Extension client libra
ii  zlib1g                  1:1.2.3.3.dfsg-5 compression library - runtime

libpango1.0-0 recommends no packages.

-- no debconf information