I've yet to see Windows connect to both 2.4 and 5GHz channels as you noted. Here it shows both on my WiFi connections list (not to be confused with which it is connected to.)
Win 7 machine with USB wireless network adapter,
Netgear 6250 wireless router with both 2.4 and 5g bands.
once upon a time the win 7 machine displayed both connections simultaneously. now it displays one or the other, but not both at the same time.
was the router switching from one to the other depending upon unknown criteria? or was it adding bandwidth from both bands?
and how do i get it to use both simultaneously?