Well, today I could test this on another machine. And the same buggy behaviour...  GUI hangs.

2007/10/28, Jakub Jelinek <jakub@redhat.com>:
On Sun, Oct 28, 2007 at 11:36:42PM +0100, Guido Ledermann wrote:
> Did it and I get
>
> [root@cookie ~]# valgrind system-config-users
> ==3131== Memcheck, a memory error detector.
> ==3131== Copyright (C) 2002-2007, and GNU GPL'd, by Julian Seward et al.
> ==3131== Using LibVEX rev 1732, a library for dynamic binary translation.
> ==3131== Copyright (C) 2004-2007, and GNU GPL'd, by OpenWorks LLP.
> ==3131== Using valgrind-3.2.3, a dynamic binary instrumentation framework.
> ==3131== Copyright (C) 2000-2007, and GNU GPL'd, by Julian Seward et al.
> ==3131== For more details, rerun with: -v
> ==3131==
> Gtk-Message: (for origin information, set GTK_DEBUG): failed to retrieve
> property `GtkTreeView::odd-row-color' of type `GdkColor' from rc file value
> "((GString*) 0x9197c30)" of type `GString'
> *** glibc detected *** /usr/bin/python2: double free or corruption (out):
> 0xbf9f1cf8 ***

Oops, that just traced consolehelper.
Try
PYTHONPATH=/usr/share/system-config-users valgrind /usr/bin/python /usr/share/system-config-users/system-config-users.py
instead.

        Jakub