I have a problem with TDM400p used in singapore and with two PSTN lines, it works fine and good with asterisk 1.2.17 + zaptel 1.2.16 except one point,
when i call in one PSTN line, one of the extensions ringing, and no one picks up the call, then the call will forward to the people's cell phone through another PSTN line, however, the people does not pick up the call as well, then i hang up my cell phone. And this time i could not call in neither the people call out. and all others like IAX trunk call and internal extensions calls are still fine.

show channels said the two lines are still active which means they did not hang up.
Any one knows whether it's a bug of zaptel or anything wrong with my side?

my zapata.conf

; Zapata telephony interface
;
; Configuration file

[trunkgroups]
[channels]
musiconhold=default
language=en
rxwink=250 ; Atlas seems to use long (250ms) winks
;
; Whether or not to do distinctive ring detection on FXO lines
;
;usedistinctiveringdetection=yes

callerid=asreceived
usecallerid=yes
;sendcalleridafter=2
;cidsignalling=v23; bell for us, v23 for uk, dtmf for denmark, sweden, and netherlands
;cidstart=polarity; ring or polarity signal the start of caller ID
hidecallerid=no
callwaiting=yes
callwaitingcallerid=yes
;restrictcid=no
;usecallingpres=yes

echocancel=yes
threewaycalling=yes
transfer=yes ;flash-hook call transfer
cancallforward=yes
callreturn=no ; *69
useincomingcalleridonzaptransfer=yes
echocancelwhenbridged=no
echotraining=300
rxgain=8.5
txgain=-1.0
callprogress=no
busydetect=yes
busycount=5
;hanguponpolarityswitch=yes
immediate=no
jitterbuffer=4 ; 4 is default
;faxdetect=both
faxdetect=incoming
;faxdetect=outgoing
;faxdetect=no

#include zapata_additional.conf
signalling=fxo_ls
context=from-internal
group=1
channel => 1

signalling=fxo_ls
context=from-internal
group=1
channel => 2

signalling=fxs_ls
context=from-zaptel
group=0
channel => 3

signalling=fxs_ls
context=from-zaptel
group=0
channel => 4