Hi,
first you have to receive a call to be able to transfer it.
Try this from your phone:
Establish an external call. Press transfer and dial an external number and press transfer again, you should not be able to transfer that external call.
Can it be possible that what is happening with the agent?
Can someone try it and let me know if they are able to do what I have explained.
( I consider TIE lines external )
Cawho
PBX.Tech