xdmcp problem with gdm on SLED11 (openSuSE 11.1)

I’m using SLED11(openSuSE 11.1) and Gnome(gdm). I configured gdm to accept xdmcp request and started Xnest with -query option as follow:

Xnest :2 -query localhost

If I click “Disconnect” button in the greeter screen, it seems the greeter keeps crashing and nothing happens.