Reg. Bridging between two channels

Hi,

I have asterisk 1.2.7.1 with TDM2400p. It is working fine and have 22 PST lines connected to 22 channels. All of sudden i was seeing the around 16-to 18 were busy… just did the show channels and came to know like pair of channels being bridged among itself…

showing a part of Show channels screen

Zap/21-1 s@default:1 Up Bridged Call(Zap/7-1)
Zap/7-1 7038222872@epro:1 Up Dial(Zap/G1/wwwwww17038222872|

Zap/12-1 s@default:1 Up Bridged Call(Zap/13-1)
Zap/13-1 7326509121@epro:1 Up Dial(Zap/G1/wwwwww17326509121|

Zap/19-1 s@default:1 Up Bridged Call(Zap/18-1)
Zap/18-1 8185007615@epro:1 Up Dial(Zap/G1/wwwwww18185007615|

Zap/20-1 s@default:1 Up Bridged Call(Zap/16-1)
Zap/16-1 2155048921@epro:1 Up Dial(Zap/G1/wwwwww12155048921|

Default is incoming calls context adn epro is outgoing call context…

and my extensions.conf like this below

[default]

include => epro

exten => s,1,Wait(1)
exten => s,2,Answer()
exten => s,3,Background(welcome)
exten => s,4,WaitExten(10)
exten => s,5,Background(welcome)
exten => s,6,WaitExten(10)
exten => s,7,Goto(280,1)
exten => s,8,Hangup()

[epro]
include =>parkedcalls

exten => _NXXNXXXXXX,1,Dial(Zap/G1/wwwwww1${EXTEN}|20,tWw)
exten => _NXXNXXXXXX,2,Congestion()
exten => _NXXNXXXXXX,102,busy()

exten => 294,1,Dial(SIP/294,20,rtT)
exten => 294,2,VoiceMail(294@voicemail)
exten => 294,3,PlayBack(vm-goodbye)
exten => 294,4,Hangup()

exten => 218,1,Dial(SIP/218,20,rtT)
exten => 218,2,VoiceMail(218@voicemail)
exten => 218,3,PlayBack(vm-goodbye)
exten => 218,4,Hangup()

and my zapata.conf is below

[channels]
language=en
signalling=fxs_ks
usecallerid=yes
;cidsignalling=v23
cidsignalling=bell
hidecallerid=no
cidstart=ring
sendcalleridafter=1
cancallforward=yes
callwaitingcallerid=yes
callwaiting=yes
threewaycalling=yes
transfer=no
rxgain=8.5
txgain=5.0
callgroup=1
relaxdtmf=yes
pickupgroup=1
immediate=no
echocancel=yes
callerid=asreceived
group=1
context=default
;channel=> 1-16 ; Again if you only have one FXO module remove the '-4’
channel=> 1-21

i am not able to understand this situation , how the bridging happened in our system between channels, at that point of call volume is very low , just 3-4 members were on the call…

i shall be thankfull, if you can help me to find out this issue due to dial plan or due to zapchannels setting in the configuration files

Thanks in advance