I hate to be a "me too", but this problem persists through the latest Win8 64 bit driver. Gigabyte Z87X-UD3H connected to HDMI, just like a previous poster - and the HDMI display will not sleep. I have two identical displays with one on the DVI port, which sleeps just fine. This is obviously a problem with the HDMI on these intel display adapters. Unfortunately, the only driver for me to roll back to is the previous one from March, which also has the issue.
I cannot believe that this problem has not been fixed yet!