PSTN Disconnect Problem - Rhino R8FXX-EC

I have a Rhino R8FXX-EC card with one FXO module with two ports. It's running on Trixbox CE 2.4.2 with Asterisk 1.4.18. The Rhino card runs firmware 1.c.

The problem is that in most cases, about 90%, of the time Asterisk does not detect when the remote caller hangs-up the phone.

I called the phone company and asked about the phone line configuration. They said the line is loopstart with reverse polarity disconnect and something about 500ms. They also said they had disconnect supervision but that the local phone company that provides the physical line might not pass it on properly, not sure what this means. I am using one of those local service providers that use the phone lines from the local Bell company, BellSouth in South Florida in this case.

So I configured zaptel.conf like this

# Span 1: Rhino RCB8FXX/1 "Rhino RCB8FXX/1"
fxsls=1
fxsls=2

# Global data

loadzone = us
defaultzone = us

And zapata.conf like this
[channels]

language=en
context=from-zaptel
signalling=fxs_ls
rxwink=300 ; Atlas seems to use long (250ms) winks
;
; Whether or not to do distinctive ring detection on FXO lines
;
usecallerid=yes
hidecallerid=no
callwaiting=no
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=no
rxgain=0.0
txgain=0.0
group=0
callgroup=1
pickupgroup=1
immediate=no
faxdetect=incoming
hanguponpolarityswitch=yes

zapata-channels.conf looks like this

; Span 1: Rhino RCB8FXX/1 "Rhino RCB8FXX/1"
;;; line="1 FXO/1/0"
signalling=fxs_ls
hanuponpolarityswitch=yes
callerid=asreceived
group=0
context=from-pstn
channel => 1
context=default

;;; line="2 FXO/1/1"
signalling=fxs_ls
hanguponpolarityswitch=yes
callerid=asreceived
group=0
context=from-pstn
channel => 2
context=default

I had hoped the hanguponpolarityswitch would be the only thing needed but it does not seem to make a difference.

In one of the posts in this forum I read that Asterisk will NOT detect a hangup if the caller is in a Queue or IVR. In my case each caller goes into a Queue immediately and I am wondering if that might be the problem instead of the Rhino card configuration.

Can anyone point me in some troubleshooting direction? Any help is greatly appreciated. Up until now I had only used SIP Trunk providers and that worked great but in this case I need to use a PSTN.

Thanks
Dan