upgrade from 11.3 to 11.4 breaks startup of some X11 apps in GLIB when being su'ed to root.

I'm using xfce desktop, logged in as normal user. then i "su" to root in xterm.
as root starting wpa_gui (see #680573) and emacs crash the same way:

harald # wpa_gui 
**
GLib-GIO:ERROR:gdbusconnection.c:2279:initable_init: assertion failed: (connection->initialization_error == NULL)
Aborted (core dumped)

harald # emacs
**
GLib-GIO:ERROR:gdbusconnection.c:2279:initable_init: assertion failed: (connection->initialization_error == NULL)
Fatal error (6)Aborted (core dumped)


from "gdb emacs-gtk"

[New Thread 0x7fffef2cc700 (LWP 31304)]
**
GLib-GIO:ERROR:gdbusconnection.c:2279:initable_init: assertion failed: (connection->initialization_error == NULL)

Program received signal SIGABRT, Aborted.
0x00007ffff385edb7 in kill () from /lib64/libc.so.6
(gdb) where
#0  0x00007ffff385edb7 in kill () from /lib64/libc.so.6
#1  0x00000000004e2ff5 in abort ()
#2  0x00007ffff64b35b2 in g_assertion_message () from /lib64/libglib-2.0.so.0
#3  0x00007ffff64b3b40 in g_assertion_message_expr () from /lib64/libglib-2.0.so.0
#4  0x00007ffff2cbef45 in ?? () from /lib64/libgio-2.0.so.0
#5  0x00007ffff2cbf841 in g_bus_get_sync () from /lib64/libgio-2.0.so.0
#6  0x00007ffff41fb15d in ?? () from /usr/lib64/libgconf-2.so.4
#7  0x00007ffff41fb3f2 in gconf_activate_server () from /usr/lib64/libgconf-2.so.4
#8  0x00007ffff4204e44 in ?? () from /usr/lib64/libgconf-2.so.4
#9  0x00007ffff4205542 in ?? () from /usr/lib64/libgconf-2.so.4
#10 0x00007ffff4205941 in ?? () from /usr/lib64/libgconf-2.so.4
#11 0x00007ffff4208952 in gconf_engine_get_fuller () from /usr/lib64/libgconf-2.so.4
#12 0x00007ffff4208cfc in gconf_engine_get_entry () from /usr/lib64/libgconf-2.so.4
#13 0x00007ffff420b99e in ?? () from /usr/lib64/libgconf-2.so.4
#14 0x00007ffff420e03d in ?? () from /usr/lib64/libgconf-2.so.4
#15 0x00007ffff420e783 in gconf_client_get_string () from /usr/lib64/libgconf-2.so.4
#16 0x00000000004d19e9 in ?? ()
#17 0x00000000004a64d8 in ?? ()
#18 0x00000000004b2cc7 in ?? ()
#19 0x000000000055bcce in ?? ()
#20 0x00000000005965b5 in ?? ()
#21 0x000000000055de0d in ?? ()
#22 0x000000000055ba12 in ?? ()
#23 0x00000000005965b5 in ?? ()
#24 0x000000000055d90d in ?? ()
#25 0x000000000055e55e in ?? ()
#26 0x00000000005956b2 in ?? ()
#27 0x000000000055de0d in ?? ()
#28 0x000000000055ba12 in ?? ()
#29 0x00000000005965b5 in ?? ()
#30 0x000000000055de0d in ?? ()
#31 0x000000000055dfa6 in ?? ()
#32 0x000000000055d5c3 in ?? ()
#33 0x00000000004eb3f0 in ?? ()
#34 0x000000000055ae7f in ?? ()
#35 0x00000000004ee94e in ?? ()
#36 0x000000000055af97 in ?? ()
#37 0x00000000004ee9e8 in ?? ()
#38 0x00000000004eee1c in ?? ()
#39 0x00000000004eef94 in ?? ()
#40 0x00000000004e40ef in ?? ()
#41 0x00007ffff384abfd in __libc_start_main () from /lib64/libc.so.6
#42 0x0000000000414179 in ?? ()
#43 0x00007fffffffd948 in ?? ()
#44 0x000000000000001c in ?? ()
#45 0x0000000000000001 in ?? ()
#46 0x00007fffffffdeb3 in ?? ()
#47 0x0000000000000000 in ?? ()
(gdb) 


emacs-x11 starts up fine, only emacs-gtk crashes.