USB keyboard power buttons cannot turn the box on because when the box is off there is no power to the USB ports. You need the original IR remote for power on/off.
So this isn't really a bug.
The Himedia boxes don't have a suspend mode, which would be a way of simulating on/off with a USB device. I have suggested to Himedia that a suspend mode be implemented which could be mapped to the power on/off button on USB keyboards.