Created attachment 848170 [details]
File: backtrace

Created attachment 848171 [details]
File: environ

I have similar error:

$ LANG="C" meld 5625.txt 9999.txt 
Traceback (most recent call last):
  File "/usr/local/bin/meld", line 178, in <module>
    main()
  File "/usr/local/bin/meld", line 170, in main
    new_window = app.parse_args(sys.argv[1:])
  File "/usr/lib64/meld/meld/meldapp.py", line 169, in parse_args
    tab = open_paths(args, options.auto_compare, options.auto_merge)
  File "/usr/lib64/meld/meld/meldwindow.py", line 796, in open_paths
    tab = self.append_diff(paths, auto_compare, auto_merge)
  File "/usr/lib64/meld/meld/meldwindow.py", line 746, in append_diff
    return self.append_filediff(paths, merge_output=merge_output)
  File "/usr/lib64/meld/meld/meldwindow.py", line 703, in append_filediff
    doc = filediff.FileDiff(app.prefs, len(files))
  File "/usr/lib64/meld/meld/filediff.py", line 312, in __init__
    self.set_num_panes(num_panes)
  File "/usr/lib64/meld/meld/filediff.py", line 1836, in set_num_panes
    w.associate(self, self.textview[i], self.textview[i + 1])
  File "/usr/lib64/meld/meld/linkmap.py", line 58, in associate
    pixbuf_apply0 = load("button_apply0")
  File "/usr/lib64/meld/meld/linkmap.py", line 57, in <lambda>
    load = lambda x: icon_theme.load_icon(x, self.line_height, 0)
glib.GError: No XPM header found

$ emerge -pv meld
dev-util/meld-1.8.5
$ eselect python list
Available Python interpreters:
  [1]   python2.7 *
$ uname -a
Linux machine 3.14.18-calculate #1 SMP PREEMPT Wed Sep 17 15:15:41 UTC 2014 x86_64 Intel(R) Core(TM)2 Quad CPU Q9650 @ 3.00GHz GenuineIntel GNU/Linux

i don't know is it related, or not, but similar string exists in this file:
https://www.imagemagick.org/subversion/librsvg/trunk/gdk-pixbuf/gdk-pixbuf/io-xpm.c

upstream bugtracker doesn't shows such bug:
https://bugzilla.gnome.org/buglist.cgi?product=meld
but the version of meld is very old

After installing =dev-util/meld-3.12.2:

 * Repository: gentoo
 * Maintainer: gnome
 * USE:        abi_x86_64 amd64 elibc_glibc kernel_linux python_targets_python2_7 userland_GNU

my problem dissapered,

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