Actually, it does work ! The trick to it is that you have to remove the power cable before you activate full power off.
The thing that's going on here is that the Cinera was designed so that it boots automatically when it is connected to the AC adapter. Therefore if you try and use power off while it is still connected, as soon as it goes full off, it reboots again due to the AC adapter being connected.
The solution to this is to disconnect the Cinera before power off.
I have discussed this with Stefan some months ago and, as Peter mentioned, they will modify that so the "on" button will need to be pressed even after connecting the Cinera to AC and "power off" mode will also work when connected.