Same here.. Just tested it.
Power off from X5 remote is a proper power off (since I have powerkey definition set that way).
But if I turn off my monitor (which is where the X5 is presently connected), about 5 seconds later, the light in front of the X5 goes RED. Turn on monitor and before monitor even has time to turn LCD on, the X5 is already powered up, led is blue, and image is ready. So it obviously goes into suspend. I checked and under CEC control, I have CEC Switch enabled, and the Device auto power off is also enabled (but it does not power off, it goes to suspend.
For me it does not bother me one way or another. I usually do a full power off out of habit from ages ago, since there were funny behavior over time. I have not tried the X5 long enough using suspend to see if there are still strange behaviors after a while. I always assumed it was due to all sorts of strange states, memory leaks and other unexpected states, but I guess time will tell. Guess "if" it is an option maybe they can add a dropdown/submenu to the "Device auto power off", so we can select "disable, power off, or suspend".
@PapaS you say you have 2 options, shutdown and restart. I am assuming you are referring to the options if you LONG press the power button on the remote. If you just quickly hit the power key on the remote, it will just do whatever is defined under the "Settings->More Settings->Powerkey Definition" There you have option for suspend, force suspend, shutdown and restart. Not sure what the difference is between suspend and force suspend however.