asterisk users - Sep 2008 - Transfer a call without announce : no sound

When we receive a call from outside (via a sangoma 104d card) and we do a
"blind transfer", that is without anouncing to the called party , we
have no
sound either way.

Exemple :

I take my cell phone to call my * box, it rings on my aastra 9113i phone, I
answer.
Then I hit the xfer buton, make my second call to another extention (it can
be either a aastra phone, nortel phone trough ciel portico, whatever.
As soon it rings I hangup or hit the xfer buton again.
Then the bridged call between the other extension and the zap channel have
no sound either way.

If I wait for the called party to answer and announce the transfer, all is
fine.

I've had report of sound one way also, but I wasn't able to reproduce.

Here's the log from my console :

   -- SIP/224-09e0f098 answered Zap/1-1
    -- Started music on hold, class 'default', on Zap/1-1
    -- Executing [225 at cybercat:1] Macro("SIP/224-09e1d728",
"ael-std-exten|225|SIP/225") in new stack
    -- Executing [s at macro-ael-std-exten:1] Set("SIP/224-09e1d728",
"ext=225") in new stack
    -- Executing [s at macro-ael-std-exten:2] Set("SIP/224-09e1d728",
"dev=SIP/225") in new stack
    -- Executing [s at macro-ael-std-exten:3]
Answer("SIP/224-09e1d728", "") in
new stack
    -- Executing [s at macro-ael-std-exten:4] NoOp("SIP/224-09e1d728",
""Nicolas Ross" <224>") in new stack
    -- Executing [s at macro-ael-std-exten:5] Wait("SIP/224-09e1d728",
"0.5")
in new stack
    -- Executing [s at macro-ael-std-exten:6] Dial("SIP/224-09e1d728",
"SIP/225|15") in new stack
    -- Called 225
    -- SIP/225-09e73388 is ringing
    -- Stopped music on hold on Zap/1-1
  == Spawn extension (macro-ael-std-exten, s, 6) exited non-zero on
'SIP/224-09e1d728<ZOMBIE>' in macro 'ael-std-exten'
  == Spawn extension (macro-ael-std-exten, s, 6) exited non-zero on
'SIP/224-09e1d728<ZOMBIE>'
    -- SIP/225-09e73388 answered Zap/1-1

Any ideas ?