This kind of relates to a post i done yesterday, mIRC has a new option to do /who onjoin, options -> IRC -> options
now, on plain mIRC the switch works, but i always do a /who onjoin in my script, and it relays everything nice and tidy and matching to my script in the status window, but the default switch doesn't turns it on or off, now i scripted it, i had to make my own switch, but also i've joined large channels in excess of 1000 users and i've never flooded off, maybe lagged by a few seconds.