//var -s %a = $chr(55384), %b = $chr(56320) | echo -a %a -- %b -- %a $+ %b -- %b $+ %a
Both %a $+ %b and %b $+ %a produce two (unassigned) characters, for me. My best guess is that mIRC is letting Windows do the UTF-16 dirty work, and Wine doesn't support it.
(This is in mIRC 7.10
under Wine 1.0.1
under MEPIS 6.5 (a Debian based Linux OS).)