I have a surface pro 3 with docking station. I have a WD portable USB hard drive plugged into the dock. While docked, if the surface goes to sleep or if I actually shut it down, the attached hard drive will also go to sleep and stop spinning. However, if I remove the surface from the dock, the hard drive will actually turn itself back on and spin forever while attached to the empty dock. The hard drive is powered by the USB bus and does not have an external power adapter. How do I stop this? When there is no surface in the dock, the external hard drive should idle.