It’s a minor issue. One that should be fixed to prevent confusion.
I would speculate kde powerdevil does not work with virtual hardware. But it’s in my opinion not useful to have power saving tools inside a VM anyhow. It’s just confusing for users to look into their VM and see that the “screen” is back. Power saving something that, if desired, should be done on the host.
Can you reliably reproduce this?
If so, to get rid of this message, please test the following command. That should prevent kde powerdevil from starting up.
Perhaps that’s a solution suitable for further releases of Whonix. (Technically speaking, using config-package-dev’s hide operation to move /usr/share/kde4/services/kded/powerdevil.desktop out of the way.)
But then under System Settings --> Power Management, we would get this:
Power Management configuration module could not be loaded.
The Power Management Service appears not to be running.
This can be solved by starting or scheduling it inside "Startup and Shutdown"
And therefore another bug report. Damn.
Another option. It will be “fixed” in Whonix 11, because in Whonix 11 the upower package gets installed by default. Then power management in a VM would be functional. Without any error messages. But useless and confusing in VMs as I think as said above.
So another solution for you, for now, would be to “sudo apt-get install upower”.
Maybe a package that gets only installed in VMs that disables kde power saving functions would be the way to go.