I have exactly the same situation (GDM running KDE over XDMCP on Ubuntu 6.06 with all updates applied, as of 21 March 2007) and GDM crashes every time a remote user logs out from KDE. This doesn't happen with Gnome or XFCE. I have to run sudo /etc/init.d/gdm restart to get it back again.
Afraid I can't add anything more useful than confirming this.
I have exactly the same situation (GDM running KDE over XDMCP on Ubuntu 6.06 with all updates applied, as of 21 March 2007) and GDM crashes every time a remote user logs out from KDE. This doesn't happen with Gnome or XFCE. I have to run sudo /etc/init.d/gdm restart to get it back again.
Afraid I can't add anything more useful than confirming this.