I don't quite see how immediately giving a PC power also presses the actual ON switch of the computer.
it is the same as a bulb. if it is already on, the wemo switch will work but if you turn it off by the switch, then like the bulb, the wemo switch will not work.
that was why I asked what their setting was in power management for the power switch. maybe that is where the difference may be.
as I already said, I done nothing extra to make it work. the only thing different than (i think) you and most others here is I run linux mint.