USB3 external hd allows power to back into computer

I have a hp desktop running win7/64 and have added a usb3 external hard drive. I find that the external wallwart power for the hard drive goes through the usb3 cable and into the computer. I discovered this when I noticed the lights on the front of the computer including the light on the power switch remained on even though the computer is completely shut down, I believe this is not supposed to happen and could cause damage to the computer. It may even produce a doubling of voltage on the usb buss under some circumstances. Isn't this an improper setup? Shouldn't the 2 power connections on the hard drive end of the cable be disconnected ?? Anyone familiar with this?:confused..

 

Not Right!! See if you can get an RMA, it should not have any feed back!

 

Thanks old phil
I agree but store geeks and others at other forums do not seem to have a clue