asterisk users - May 2004 - ISDN & Voicemail: Strange Behaviour

Hi,

whenever I include a "Ringing" Line in some Voicemail Extension
I get an error when a call from the outside (via ISDN) comes in,
but it works when an internal (SIP-phone) calls the extension.

Here is my configuration for testing:

------------extensions.conf------------
 [isdnext]
; strep external "101", our number and leave only extension
exten => _101XX.,1,Goto(default,${EXTEN:3},1)

 [default]

exten => _50XXX,1,VoiceMailMain(${EXTEN:2})

exten => _51XXX,1,Ringing
exten => _51XXX,2,VoiceMailMain(${EXTEN:2})
------------extensions.conf------------

(just fyi: Voice-Mailbox "121" exists)

1. when local SIP-phone calls "50121" or "51121" it
   gets the voicemail-password prompt. correct behaviour.

2. when external call via ISDN for "101-50121" comes in it
   gets the voicemail-password prompt. correct behaviour.

3. when external call via ISDN for "101-51121" comes in, the
   line ist hung-up immediately and the following error
   messages are on the * console:

-------------------------------------------
    -- creating pipe for PLCI=0x101 msn = *
       > sent ALERT_REQ PLCI = 0x101
    -- Executing Goto("CAPI[contr1/10151121]",
"default|51121|1") in new stack
    -- Goto (default,51121,1)
    -- Executing Ringing("CAPI[contr1/10151121]", "") in new
stack
    -- Executing VoiceMailMain("CAPI[contr1/10151121]",
"121") in new stack
    -- CAPI Answering for MSN 0151121
May 13 20:22:11 ERROR[1114581936]: chan_capi.c:860 capi_write: dont know how to
write subclass 4
May 13 20:22:11 WARNING[1114581936]: res_adsi.c:163 adsi_careful_send: Failed to
carefully write frame
May 13 20:22:11 WARNING[1114581936]: res_adsi.c:205 __adsi_transmit_messages:
Unable to send CAS
May 13 20:22:11 WARNING[1114581936]: file.c:537 ast_readaudio_callback: Failed
to write frame
    -- Playing 'vm-password' (language 'en')
May 13 20:22:11 WARNING[1114581936]: app_voicemail.c:2764 vm_execmain: Unable to
read password
  == Spawn extension (default, 51121, 2) exited non-zero on
'CAPI[contr1/10151121]'
    -- CAPI Hangingup
       > sent DISCONNECT_B3_REQ NCCI=0x10101
       > sent DISCONNECT_REQ PLCI=0x101
    -- removed pipe for PLCI = 0x101
-------------------------------------------


Bug or Feature ?


regards
Andreas