I am having same issue.
I am trying to configure a Call Handler option to route calls to external ext.
Call come into main Call HandlerA.   Caller chooses option 3 which is attempt to transfer to call handlerB. 
I have tried configuring transfer rule for Call Handler B to ring ext but call is not seen as a transferred call.
I have also had call handler B go to Call Handler C and configured the handler C transfer rule to go to ext.
It works when the calls are going directly to the call handler A and then after greeting Transfer to Call Handler B where transfer rule is ringing to extension.
Im thinking I have to convert Call Handler A to a Subscriber where I can choose Alt contact number for option 3.