GR64 autmatically hangs up busy voice call

We are finding that when we make an outgoing voice call from the GR64, if the remote end is busy (engaged) the GR64 terminates the call and the user does not hear the engaged tone.
With call progress notification on we get
*ECAV: 1,7,1
then immediately
*ECAV: 1,0,1,8,17

(On the previous GR47 we were using we had to issue AT+CHUP after we recieved *ECAV: 1,7,1 and in the mean time heard an engaged tone)

Is there a way we can get the GR64 to “play” the engaged tone and not to hang up the call until the user issues AT+CHUP?

Most users expect to hear an engaged tone if the remote end is busy!

Thanks
Andrew