All USB devices on the same host controller are powered on and never return to selective suspend mode when one of the USB devices is woken up on a Windows Vista-based or Windows Server 2008-based computer
On a computer that is running Windows Vista or Windows Server 2008, multiple USB devices are connected to the same USB host controller. When the USB devices on the USB host controller are in selective suspend mode, one of the USB devices is woken up. In this scenario, all USB devices on the host controller are powered on, not only the USB device that is intended to be woken up. Additionally, the USB devices that are not being used never return to selective suspend mode. Therefore, more power is consumed than necessary.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB961249.