The IP address is not being shared as it is a static IP. The IP being reported by whatismyip, ipinfo, and other sites does not match the IP being repored by 8ch. Normally I would suspect a software bug on 8ch's end but it seems like an almost-impossible bug to run into accidentally, and the traceroutes provided in the opening post in this thread clearly show BT tampering with the connection.
A shared IP would show in traceroutes as normal hops (when the packet passes through NAT routers), and it would be consistent across all ports targeted on the destination machine.
Does anyone know anything about the presumably malicious BT machine "bn-proxy1a.ealing.ukcore.bt.net", which is the source of this problem?
BT do not supply static IP adresses to residential customers, on business ones.
If you are a business user, then you are posting on the wrong forum.
Whether static or dynamic your currently provided IP will not normally change mid session and then revert back 😉