asterisk users - Apr 2007 - Attended Transfer of a queue call fails

Hi,

I'm using Grandstreams as the agents phone of a queue. Attended
transfers in a normal situation (direct call to the extension) work
fine, but when the agent has a queue call and tries to transfer it to
another sip extension the called party is hung up. 

Transfer is to pick another line on the Grandstream, dial the other
extension, wait for a pickup, and then press the transfer button + the
parked line on the Grandstream. I can reproduce that in several
asterisk, and the inbound call comes from an mISDN channel or a sip
channel, and with similar results using a SNOM 190 terminal

Asterisk is a 1.2.14-BRIstuffed-0.3.0-PRE-1x built on Gentoo

any ideas?

best regards
-- 
Alexander