You will find this is a caller ID thing. Try adjusting outbound caller ID to be the BTN. I have also found sometimes it's carrier specific and have made the VE a Mobile extension. Also check your ISDN settings on your PRI sometimes changing NI-2 to Standard or vice versa makes it work. This is normally a B-channel issue on a sip box and for whatever reason the NEC makes subtle changes when you forward in different ways.