Hi again Crusey83,
Just did some more checking on the Haswell NUCs. It appears that you should enable Deep S4/S5 on the Power menu to make sure that USB devices are not powered at all when the NUC is turned off.
I am not seeing any issues though with Windows 8.1 recognizing the external drive in my testing. So, please send in the information I requested earlier, if you can.
Thanks,
Lois