I'm not in the Windows 8 hate club, but I do believe this is an issue that started with Windows 8 and has yet to be corrected in Windows 8.1. Neither of the motherboards I have run with Win8/8.1 have Atheros chipsets. My main board now has an Intel Ethernet chip. Both of those boards need to have IPv6 disabled to allow the computer to sleep. Those same boards sleep fine under Windows 7 / Linux so I have to assume there is some type of issue specific to Windows 8. I imagine the issue will be patched at some point, but until then the solution is pretty simple.