Strange WiFi problems after power blips

Greetings,
Can anyone give me some tips on how to resolve, or at least investigate, a strange problem with WiFi?

There are two houses involved. I broadcast from two APs at one house, and can receive one of the signals at a guest house.

I have some guests renting the second house who brought several PCs and phones--both cell and wireless IP phones. After a couple of very brief power blips, some but not all of their devices no longer see the SSID. Everything was fine before the power blip.

However, walking a couple of those devices over to my house, they are able to see and connect to the other AP.

It appears that both SSIDs are being broadcast, and all hardware is able to connect to something.

We installed inSSIDer on a couple of their PCs (both HP laptops, but not identical), and same thing. One PC can see both SSIDs and the other can only see one SSID.

Affected devices include
. HP laptop running Win7
- Android phone
- Cisco 9971 wireless IP phone
- Cisco 7925 wireless IP phone

I posted additional details on Ubuntu fourms but so far no help. I can't post a link yet, but more details are at UbuntuForums.org/showthread.php?p=11631883#post11631883

Both myself and my guest have technical backgrounds, but we're scratching our heads over this. If this can't be answered, can someone at least say *why* it can't be answered?
Thank you very much,

My guest remembered that when things were working the AP was broadcasting on channel 11, but inSSIDer was now showing channel 13. When I forced the AP to broadcast on channel 11 (instead of "SmartSelect"), immediately the other devices were again able to see the SSID and connect.

Any ideas why this would happen to multiple devices like this?