im not sure it is a bug or if it is supposed to be this way, $serverip returns 255.255.255.255 in a disconnect event.

perhaps not needed, but the code to reproduce it:
on *:disconnect:{ echo -s $serverip }

i wanted to echo the server name and ip when getting disconnected when i noticed this, scripted around it for now.

btw, im using mirc 6.15 on winXP pro

I get 255.255.255.255 both while online and offline.

i would think it wouldnt show the server ip because on disconnect takes place after the disconnection from a server, so if you are not connected to anything then why would it show an ip?

on disconnect takes place when you get disconnected, not after.
if $server and $port work, i dont see why $serverip shouldnt work in that event. in addition it would be great if mirc would show by default something like:

[17:38:14] * Disconnected from irc.server.org (12.34.56.78) on 6667