Edubuntu 12.04 LTSP - Fat clients hangs on shutdown with Kernel 3.8 and higher

[X-Dimension]

Hello,

we are using LTSP with Edubuntu 12.04 for some years now and it works 
fine except a
shutdown problem, we had over one year ago with our Zotac Zbox clients.
We had fixed this problem by using a patched version of LDM that is 
starting "poweroff -fp" instead
of "poweroff" and also with an old "ltsp-shudown.conf" from Edubuntu 
11.xx, that also forces
to use "poweroff -fp". The ltsp-shutdown.conf was needed to fix the 
shutdown problem, when using Epoptes to power off the clients.

This Workaround was working fine with the Zotac Zbox, but we have now 
some Shuttle DS437 clients, that needs a newer Kernel version to run 
smoothly.
After updating our LTSP images to Kernel 3.8.x all clients hangs again 
on shutdown when using the Epoptes management tool to poweroff the clients.
The only way to successfully poweroff a client is to use the patched LDM 
version with "poweroff -fp".
After switching back to kernel 3.5.x, the shutdown problem is gone, but 
the Shuttle DS437 have some graphics problems and are running very slowly.

Can anybody help me to fix this shutdown problem when using a newer 
Kernel version?
It looks like the ltsp-shutdown.conf have no effect anymore when using 
Kernel 3.8 and later,
but i don't know why.

Thx