When using a CJK ime for example, using an european keyboard who has accents, typing accentuated characters like é or è yields a simple e, whereas typing in any editor(notepad, input box in firefox/ie/explorer) works and displays the right character.
Copy/pasting these characters in mirc does work, with the unicode support all fine.

It seems for some reason mirc will not accept(or is using a method that wont accept) any character that isnt in the current ime's default locale(or something like that). Makes utf-8 a bit useless sadly(although it does have an use when pasting various contents)