Hi Matt,
I can only report what is happening here and it could be something in the dual role of a USB port being both data transfer and power source - a friend of mine has a Fujitsu external drive powered by a 5 amp power pack and a normal single USB cable which works fine - to me this is a better way
The point of the comment on "allow the computer to turn off this device to save power" is that it is checked as the default setting
Brian