your mouse is taking power from the usb. some motherboards can recognize the usb devices that require power even if the system is off. I got Asus P5LD2 motherboard with the Logitech G7 wireless mouse and the station is always charging the battery, and taking power from usb even with the system off.
now, according your problem, your motherboard cuts all the power to the usb ports, so your mouse is resetting. during restart the power is not cut, that's why is ok with restart. see manual of motherboard about that.