When trying to select a single Japanese character by highlighting/selecting with the mouse so it may be pasted elsewhere, mIRC will copy nothing. It appears that the routine to place the selected text in the clipboard after the the MB1(MouseButton 1) is released is not invoked.

My settings were:
mIRC 6.2 Options > IRC > Messages:
checkbox: SJIS/JIS conversion unchecked, with the other 5 of the group of 6 checkboxes there checked.
Also the font setting for the channel was:
MS Gothic: Script Japanese: Display and Encode

I'm using the default IME that comes with windows xp pro.

same bug for any single caracters anyway.

This isn't a bug. mirc won't allow you to copy a single character (whether multi- or single-byte) as this would make it easier to accidentally overwrite your clipboard (stray clicks and drags).

I see, if that's the case, I am hereby requesting, an option to toggle that, because I am in a Japanese learning channel where copying a single character is a common activity.

Best way to suggest it would be to make a topic in the Feature Suggestions forum and link this thread. This way, people actually SEE the feature suggestion. That has happened a lot over the years; people make suggestions in BUG REPORTS and nobody sees/replies to it because it's in the BUG fix section

It is always possible to select two charactors including the one needed, and delete the one that is not needed.
That said being able to turn it off would be good.
Personally it would be left needing 2 charactors being selected.