Changing port number

I posted a while back about seemingly changing ports on the same host.

While using Phex 3.2, I browsed the same host 4 times in about 5 minutes. The first browse used remote port # 32608 (the host was using LW 4.14 Pro)
The next 3 browses used remote port # 21736

I checked the TCP header info and found this line in the remote host header X-FWTP: 21736. Ive never seen that line before.

I think this is some kind of redirect to a new port due to a firewall configuration?

I noticed that all downloads from the host also came through this port 21736.

Is it normal for the listening or "browse" port to redirect traffic to a new port?
Thanks
Dave