Why isn't the AR06 not allowing my PC to power down?
BIOS features vary across manufacturers, etc. There may be a feature in your BIOS which is along the lines of "Power On after power failure." This "feature" started to be added when soft switches were added to computers. It's designed so that when your computer loses power, it will come back on the next time power is at the plug so-to-speak.
Also, the ecoficient outlet may not be compatible and/or have some inconsistent operation with some power supplies within some computers. I'm familiar with this type of energy saving outlet/power strip, but not the intricacies of the brand, etc.