While this reliability issue easily can be workarounded on the Android devices by disabling the WIFI powermanagement of the device - WIFI connection becomes stable and fast after that - on cost of higher battery drain.
So this issue seems to be more Android WIFI powermanagement behaviour related and not directly Sophos WIFI related, I do not consider it a UTM9.x bug. But probably there is a way to keep such devices reliable WIFI connected without sacrificing the powersaver option on the android JB devices ?
Also see this mentioned issue in other Android/google blogs
Wie genau spart "WLAN-Optimierung" Strom? - Android-Hilfe.de
https://code.google.com/p/android/issues/detail?id=40065
Part from my UTM's wireless.log. Device connects, and gets deauthenticated a few secs later "due inactivity", but the device is in use then...
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: authentication OK (open system)
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: authenticated
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: association OK (aid 1)
2013:04:29-17:26:29 192.168.10.111 awelogger[2412]: id="4104" severity="info" sys="System" sub="WiFi" name="STA association" ssid="22.718.99y" ssid_id="WLAN0.0" bssid="00:1a:8c:0b:34:10" sta="20:64:32:54:ee:57" status_code="0"
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: associated (aid 1)
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-ASSOCIATE.indication(20:64:32:54:ee:57)
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-DELETEKEYS.request(20:64:32:54:ee:57)
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: event 1 notification
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: start authentication
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.1X: unauthorizing port
2013:04:29-17:26:29 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: sending 1/4 msg of 4-Way Handshake
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: received EAPOL-Key frame (2/4 Pairwise)
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: sending 3/4 msg of 4-Way Handshake
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: received EAPOL-Key frame (4/4 Pairwise)
2013:04:29-17:26:30 192.168.10.111 awelogger[2412]: id="4101" severity="info" sys="System" sub="WiFi" name="STA connected" ssid="22.718.99y" ssid_id="WLAN0.0" bssid="00:1a:8c:0b:34:10" sta="20:64:32:54:ee:57"
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.1X: authorizing port
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 RADIUS: starting accounting session 517E8690-00000008
2013:04:29-17:26:30 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: pairwise key handshake completed (RSN)
2013:04:29-17:27:21 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 WPA: event 2 notification
2013:04:29-17:27:21 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.1X: unauthorizing port
2013:04:29-17:27:21 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: disassociated
2013:04:29-17:27:21 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-DISASSOCIATE.indication(20:64:32:54:ee:57, 8)
2013:04:29-17:27:21 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-DELETEKEYS.request(20:64:32:54:ee:57)
2013:04:29-17:27:22 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 IEEE 802.11: deauthenticated due to inactivity (timer DEAUTH/REMOVE)
2013:04:29-17:27:22 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-DEAUTHENTICATE.indication(20:64:32:54:ee:57, 2)
2013:04:29-17:27:22 192.168.10.111 hostapd: wlan0: STA 20:64:32:54:ee:57 MLME: MLME-DELETEKEYS.request(20:64:32:54:ee:57)
2013:04:29-17:27:28 192.168.10.111 kernel: [ 9988.580000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
2013:04:29-17:27:28 192.168.10.111 kernel: [ 9988.690000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
2013:04:29-17:27:29 192.168.10.111 kernel: [ 9988.960000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
2013:04:29-17:27:29 192.168.10.111 kernel: [ 9989.070000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
2013:04:29-17:27:29 192.168.10.111 kernel: [ 9989.480000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
2013:04:29-17:27:29 192.168.10.111 kernel: [ 9989.580000] wlan0: dropped frame to 20:64:32:54:ee:57 (unauthorized port)
In the other hand I also have to mention, that UTM9.1 feels much snappier than 9.006, and overall WIFI throughput for other devices subjective seems to be better (copying large files shows higher effective throughput)