asterisk users - Oct 2011 - device state of SIP device is stucked into NOT_INUSE, and cannto be reverted to unavailable

Hello

Have a setup of asterisk with realtime SIP devices.
Trying to organise monitoring of my SIP devices. Once device
registered, its state becomes NOT_INUSE (result of
DEVICE_STATE(SIP/device) function).
Simulating of device breakage - powerdown it.
Waiting for a while (minute or two), retrieving
DEVICE_STATE(SIP/device) again - no changes! Awaited UNAVAILABLE.

doing from CLI:
sip qualify peer device load
no result.

What I did not configured?

My sip.conf
[general]
context = default

allowguest = no
bindport = 5060
bindaddr = 0.0.0.0

allowexternaldomains = no
allowoverlap = yes
allowsubscribe = yes
allowtransfer = yes
alwaysauthreject = no
autodomain = no
callevents = no
canreinvite = no
checkmwi = 10
compactheaders = no
defaultexpiry = 120
domain=sop-korniychuk
domain=172.30.8.13
domain=172.30.8.13:5060
dumphistory = no
externrefresh = 10
g726nonstandard = no
notifyringing = yes
srvlookup = yes
t1min = 100
t38pt_udptl = no
;tos_audio = none
;tos_sip = none
;tos_video = none
trustrpid = no
useragent = Asterisk PBX
usereqphone = no
videosupport = no
disallow = all
allow = alaw
type = friend
host=dynamic
context = noop-context
dtmfmode=rfc2833
nat=no
rtcachefriends=yes
qualify=10000
deny=0.0.0.0/0.0.0.0
permit=172.30.8.0/255.255.255.0

regards, Yaroslav