asterisk users - Mar 2004 - OT Sipura: Sipura doesn't "see" * hangup PSTN line

I have an Siemens two-line base station connected as follows:

Line 1:  Sipura SPA-2000 Line 1
Line 2:  Sipura SPA-2000 Line 2

I have a single POTS line (Verizon) connected to a Digium X100P card.

[Config excerpts are below]

Issue:  Calling into the * server rings the Siemens base station as 
expected.  After about 20 seconds the Siemens base station answers the 
call and sends the call to voicemail (I know I should use VM in * but my 
spouse isn't yet ready for that...).

   == Spawn extension (from-verizon, h, 1) exited non-zero on 'Zap/1-1'
     -- Hungup 'Zap/1-1'

Then the caller hangs up.  Asterisk "sees" this hangup and disconnects
the PSTN line (I confirm this with a monitor phone on the POTS line).

Asterisk sends the SIP BYE command, and receives the OK response from 
the Sipura.  For some reason the Sipura doesn't hangup line 1 and, as a 
result, every message on the Siemens base station has a ~15 second 
Congestion tone trailer.

Any ideas?  Most likely the answer is "bug in Sipura, move quickly to 
*-based VM, right?  :^)

Relevant zapata.conf entry:
-------------------------------------
[channels]
language=en
context=from-verizon
signalling=fxs_ks
usecallerid=yes
echocancel=yes
echocancelwhenbridged=yes
channel => 1

Relevant extensions.conf entry:
-------------------------------------
[from-verizon]
exten => s,1,Dial(SIP/sipura_line1)
exten => s,2,Hangup
exten => h,1,Hangup
exten => i,1,Hangup

Relevant sip.conf entry:
-------------------------------------
[sipura_line1]
type=friend
username=sipura_line1
secret=XXXXXX
host=dynamic
context=from-siemens-line-1
mailbox=9000
canreinvite=no
callerid = <8885551212>

-- 
Rob Page                V: 540.361.1710
Zope Corporation        F: 703.995.0412