Comment 2 for bug 373680

Try this and see if you get the same result:
$ while : ; do iwconfig ath0|grep 'Freq' ;sleep 1; done

I get:
...snip...
          Mode:Managed Frequency:2.432 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:2.442 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.18 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.26 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.5 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.58 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.68 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:5.785 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:2.432 GHz Access Point: 00:22:57:53:DB:80
          Mode:Managed Frequency:2.432 GHz Access Point: 00:22:57:53:DB:80
...snip...

The frequencies indicate that this is an 802.11n scan. I suspect it is being initiated by wpa_supplicant because running wpa_supplicant with the '-ddd' option provides this at the same time the 802.11n scan happens:

Setting scan request: 0 sec 0 usec
Starting AP scan (broadcast SSID)
Scan requested (ret=0) - scan timeout 30 seconds
RTM_NEWLINK: operstate=1 ifi_flags=0x11043 ([UP][RUNNING][LOWER_UP])
RTM_NEWLINK, IFLA_IFNAME: Interface 'ath0' added
Wireless event: cmd=0x8b19 len=8
Received 1764 bytes of scan results (5 BSSes)
CTRL-EVENT-SCAN-RESULTS
Selecting BSS from priority group 0
Try to find WPA-enabled AP
0: 00:22:57:53:db:80 ssid='MyNet' wpa_ie_len=22 rsn_ie_len=20 caps=0x11
   selected based on RSN IE
   selected WPA AP 00:22:57:53:db:80 ssid='MyNet'
Already associated with the selected AP.

To have the wireless cut out for 6-7 seconds is really painfull...

linux-backports-modules-2.6.28-12-generic(2.6.28-12.13)
linux-image-2.6.28-12-generic(2.6.28-12.43)
linux-restricted-modules-2.6.28-12-generic(2.6.28-12.16)

$ modinfo ath9k
filename: /lib/modules/2.6.28-12-generic/updates/ath9k.ko
license: Dual BSD/GPL
description: Support for Atheros 802.11n wireless LAN cards.
author: Atheros Communications
srcversion: B066EA404154EA4DD8862D0
...
depends: lbm_cw-cfg80211,lbm_cw-mac80211,led-class
vermagic: 2.6.28-12-generic SMP mod_unload modversions 586
...