Edubuntu 12.04 LTSP - Shutdown and wake on LAN problems with Zotac ZBox

[X-Dimension at gmx.net]

We are using Edubuntu 12.04 with LTSP in our primary school.
As thin clients we use the Zotac ZBox Nano ID61.
One big problem is that the clients don't power off with "shutdown -h now" or "poweroff -p". They only power off when using "poweroff -fp".

Now we want to use wake on LAN to start all the clients with Epoptes, WOL itself works fine with the ZBox Nano, but when using them as an LTSP Client the "poweroff -fp" option seems to completely shutdown the network interface and WOL don't work. 

Can anybody help us to get WOL to work? 

Thx