It seems the latest mIRC simply enables as many CAP's as it can on connect, which is interfering with channel messages, for example on non-mirc irc client, you can see the following messages both as ircop and normal user on every channel when a hostname changes:

<- Amiga600 (Amiga600@B5CEFE5E.9C343252.60C7238D.IP) has left #MBC [Changing host]

But on mIRC I cannot see any of these messages, and it appears I have no control over what "CAPS" are enabled on connect, since mIRC assumes I want to enable them by default:

Caps supported: unrealircd.org/plaintext-policy=user=allow,oper=warn,server=deny unrealircd.org/link-security=2 extended-join chghost cap-notify userhost-in-names multi-prefix away-notify account-notify sasl=EXTERNAL,PLAIN tls

Caps set: extended-join chghost cap-notify userhost-in-names multi-prefix away-notify account-notify

I cannot see any Options which will allow me to choose which "CAPS" I want enabling, so if theres a way to stop this from happening, Please let me know, Thankyou.