the problem of 802.11d and Mac OSX

There seems to be a nice issue with how Macs do their 802.11d

http://jeff-with-a-g.blogspot.co.uk/2012/04/5ghz-wifi-on-your-mac-got-yo...

basically, when the Mac boots up or wakes from sleep, it looks for the first 802.11d beacon that it can find...and then uses that to decide what country it is in......which means that if theres some 3rd party AP nearby (or eg MiFi device) saying its in some other country then the Mac will change its radio rules to that country code - meaning that e.g. several 5GHz channels are no longer available.

If your site is using that channels for its 5GHz (802.11a/an/ac) - e.g. UNI-II Extended, then the client will no longer see those channels...and therefore no longer see the SSID - you may have 2.4GHz also available for that SSID but the client will now not be using the technology you want it to use. (and same issue may apply with 2.4GHz - some countries dont allow all the 1 to 11 channels that you expect to be able to use)