I've observed some weird behavior where for example if you use $chr(160) or alt+0160 (non-breaking space), mIRC would insert $chr(194)/alt+0194 before the non-breaking space.

-> irc.net.work PRIVMSG gemini :test test
<- :Gemini!Gem}test@rawr PRIVMSG Gemini :test test

Tested on mIRC 7.22 where this behaviour occurs and 6.35 where it does not.