GDM doesn't show login screen using XDMCP

[Id2ndR]

Binary package hint: gdm

System : Ubuntu Gutsy.
Display : one with intel 1280x800, other with proprietary nvidia 1280x1024.

Steps :
- login on both computers to get connected to Wireless Network. Then logout (wireless connection will still be active).
- Try to use XDMCP using Option menu
=> Screen will blank, and X logo will appear on the screen, less than one second. Then, screen will blank again and local gdm screen will be back.

Corresponding errors in /var/log/syslog :
Oct 3 11:02:10 Id2ndR-SFF gdmchooser[6424]: GLib-GObject-WARNING: /build/buildd/glib2.0-2.14.1/gobject/gsignal.c:1019: unable to lookup signal "activate" of unloaded type `GtkMenuItem'
Oct 3 11:02:14 Id2ndR-SFF gdm[5274]: WARNING: gdm_cleanup_children: child 6428 crashed of signal 11
Oct 3 11:02:14 Id2ndR-SFF gdm[5274]: WARNING: gdm_cleanup_children: Slave crashed, killing its children

I didn't find any error in Xorg logs.

[Sebastien Bacher (seb128)]

That might be a duplicate of bug #118193

[Id2ndR (id2ndr)]

No it's not a duplicate since it is able to restart. And I also can login after having activated XDMCP.
It don't work only if I try to use XDMCP (and return automatically and correctly to local GDM login screen).