Well, Hitech seems to know a reason that this would happen. I would think it would be because of all the various devices plugged in the USB chain that could cause an elevated ground potential. This is a fairly normal thing on laptops that don't use a grounded charging plug, for instance, or a system with a cheaper PSU that has attempted cable management and created a cross talk situation.
It's getting to be a fairly common thing with so many devices plugged into a single system.