asterisk users - Apr 2012 - ISDN incoming call disconnected after picking up phone

Hi,

I have been trying to find solution to this problem by googleing and 
experimenting but without success so you are my last chance.

I have asterisk 1.8.11 installation on Debian squeeze with HFC-S PCI 
ISDN interface cards (dahdi channel, zaphfc kernel driver) , Huawei USB 
3G stick, Siemens Gigaset SIP phones and IAX PC soft phone.

The problem is that when I receive call through ISDN interface and pick 
up (SIP or IAX) phone, line immediately gets disconnected.

This is what I get with pri debug on :

PRI Span: 1 > Progress Indicator (len= 4) [ Ext: 1  Coding: CCITT (ITU) 
standard (0)  0: 0  Location: Private network serving the local user (1)
PRI Span: 1 >                               Ext: 1  Progress 
Description: Called equipment is non-ISDN. (2) ]
PRI Span: 1
PRI Span: 1 < Protocol Discriminator: Q.931 (8)  len=4
PRI Span: 1 < TEI=90 Call Ref: len= 1 (reference 21/0x15) (Sent from 
originator)
PRI Span: 1 < Message Type: CONNECT ACKNOWLEDGE (15)
PRI Span: 1 Received message for call 0x89a4e68 on link 0x88a4238 
TEI/SAPI 90/0
PRI Span: 1 q931.c:8484 post_handle_q931_message: Call 21 enters state 
10 (Active).  Hold state: Idle
PRI Span: 1
PRI Span: 1 < Protocol Discriminator: Q.931 (8)  len=12
PRI Span: 1 < TEI=90 Call Ref: len= 1 (reference 21/0x15) (Sent from 
originator)
PRI Span: 1 < Message Type: DISCONNECT (69)
PRI Span: 1 < [08 02 81 90]
PRI Span: 1 < Cause (len= 4) [ Ext: 1  Coding: CCITT (ITU) standard (0) 
  Spare: 0  Location: Private network serving the
  local user (1)
PRI Span: 1 <                  Ext: 1  Cause: Normal Clearing (16), 
class = Normal Event (1) ]


So, after getting CONNECT ACKNOWLEDGE there is an immediate DISCONNECT 
received from telco.

This happens always if dialed extension is
-- SIP
    exten => ${MSN1},1,Dial(SIP/phone1)
or IAX
    exten => ${MSN1},1,Dial(IAX2/phone2)
or multiple extensions
    exten => ${MSN1},1,Dial(SIP/phone1&Dongle/dongle0/phone3)

but not if it is chan_dongle alone
    exten => ${MSN1},1,Dial(Dongle/dongle0/phone3)


Maybe it is worth mentioning that this problem started after switching 
telco. First one used simple NT device connected to the line and second 
one uses Patton IAD connected to the router.


Can you help me to find a solution to this problem?

Thanks in advance.

Best regards,

Ivo.