We've seen this on 6.4.2.2,. Most of these reports are with AP-225s with 80MHz but we don't have a strong read on that factor yet. For the case where it happens after hibernation on an MS Surface, there may be relief coming soon from Microsoft, but we've seen it on other Win8.1 systems as well. We think we'e seen a correltion with the machines being set to host authentication versus user, but we are still waiting for more solid data back on that.
(Edited to add: we've done a bit of diagnosis on the post-hibernation Surface case, and can see the system sending WiFi packets in and the AP sending reply packets back out, but the OS never sees tham, even in wireshark.)