Recently when changing the fonts for mIRC, I noticed that if I change the font via the switchbar popup menu on a minimized window, the changes for that window do not take affect.
Connect to any server and join a channel.
Minimize the status window giving the channel focus.
Right click on the status window's switchbar button and select Font...
Change the font to something clearly different from what you would normally use, press OK.
Now when you restore the status window the font dosn't appear to have change, it can be confirmed by opening the Font dialog again, it should still be using the original font.
I'm using mIRC 6.16 on WinXP Home.