Agreed that the stock "The 5 GHz band is usually more susceptible to walls and obstacles" line is moot. 5GHz may be more susceptible to dBi loss, but it also has less interference. In reality, in an indoor environment, they signals are about the same. Outdoors is a different story. It also very much depends on your antennae.
That said, I'm having this same issue with a couple of customer laptops. They're running Win 8.1. 2.4GHz works properly, 5GHz does not. If the AP is set to urge or force 5GHz - the laptops will not connect. If the laptops are set to prefer 5.2GHz, they don't connect. The clients aren't making it to the RADIUS handshake, they're dying out at:
03/12/2014 12:43:00 PM FCF8AE558EE4 DETAIL (755)Receive message from RADIUS Server: code=11 (Access-Challenge) identifier=34 length=64
03/12/2014 12:43:41 PM FCF8AE558EE4 BASIC (757)Sta(at if=wifi1.2) is de-authenticated because of notification of driver
or after
03/12/2014 12:45:35 PM FCF8AE558EE4 INFO (794)IEEE802.1X auth is starting (at if=wifi1.2)
03/12/2014 12:46:16 PM FCF8AE558EE4 BASIC (796)Sta(at if=wifi1.2) is de-authenticated because of notification of driver
I can't for the life of me understand why an 802.11ac product, made to standard doesn't work with 802.11na. Even setting the channels to 20MHz, 40Mhz Above, 40MHz Below has no change.
The clients can ONLY connect at 2.4Ghz. Intel needs to get their act together - they're better than this. 2.4GHz is too congested and 802.11ac v2 is right around the [all too expensive] corner...