DTMF pass through issue

i setup a system.structure as following

Sip client A-> Asterisk server A <-> Asterisk ServerB

Sip client A registe the Server A. Server B is a IVR server.
Client A call Server B passthrou ServerA,and get ivr.if Client A press DTMF, Server B can received well. that is good.

there are blindtransfer function on Server B,but if i make a outbound call from Client A pass through ServerA,ServerB,back to ServerA and a outbound GW to a phone. when call was connected,Sip client A press Dtmf * to start blindtransfer, nothing happied. :frowning:

then hung up the phone.Client A will going to hear the IVR,but DTMF not work any more. :frowning:.
any body can give me some suggestion.thanks a million…

thanks again.