asterisk users - Jan 2005 - No music with "Blind" transfer on GS ATA + Sipura-841

Hi there,

I have setup Asterisk with a couple of Sipura SPA-841's and Grandstream 
ATA's.

The problem is that with both of these devices the Unattended call 
transfer process seems to be just like Attended but instead you hang up 
as soon as you have dialled the number of the party your are 
transferring to.  The call transfer all works fine BUT as you complete 
your side of the transfer and the destination extension is ringing - ie. 
Caller calls you, you transfer call to another extension and hangup 
before they answer and another extension is left ringing waiting for 
someone to pickup, the inital caller has only silence and no MOH (or 
ringing).

I cannot tell wether this is a function of Asterisk (which seems to end 
MOH during bridging of the calls) or the SPA-841 / GS's but the problem 
is that doing this type of unattended transfer results in what the 
initial caller hears as a dead line and they are prone to hangup should 
the called party not answer quickly. 

I guess we could just do all transfers as attended and wait for the 
called party to answer so as to avoid this "assumed dead line" problem
but I wonder if anyone has also experienced this and or found a solution.

My Asterisk log is as follows:

asterisk*CLI>
    -- Executing Macro("SIP/201-6447", "oneline|Sip/200") in
new stack
    -- Executing SetMusicOnHold("SIP/201-6447", "random") in
new stack
    -- Executing Dial("SIP/201-6447", "Sip/200|30|tr") in
new stack
    -- Called 200
    -- SIP/200-08b4 is ringing
    -- SIP/200-08b4 answered SIP/201-6447
    -- Attempting native bridge of SIP/201-6447 and SIP/200-08b4
    -- Started music on hold, class 'random', on SIP/201-6447
    -- Executing Macro("SIP/200-eedc", "oneline|Sip/202") in
new stack
    -- Executing SetMusicOnHold("SIP/200-eedc", "random") in
new stack
    -- Executing Dial("SIP/200-eedc", "Sip/202|30|tr") in
new stack
    -- Called 202
    -- SIP/202-f8cf is ringing
    -- Stopped music on hold on SIP/201-6447 
  == Spawn extension (macro-oneline, s, 2) exited non-zero on 
'SIP/200-eedc<ZOMBIE>' in macro 'oneline'
  == Spawn extension (from-internal, 200, 1) exited non-zero on 
'SIP/200-eedc<ZOMBIE>'
    -- SIP/202-f8cf answered SIP/201-6447
    -- Attempting native bridge of SIP/201-6447 and SIP/202-f8cf

Thanks,
Justin.