I don't know if it's a bug, some commands do this. It's like /.echo. If this is a bug it's been in mIRC for a very long time, I tested on 6.15, 6.14 and 5.9 and it happens on all of those too. Perhaps there's some reason that it happens, probably because it echos information to the user (like /.echo, /.whois) rather than giving information out (unlike, for example, /.notice, /.msg, /.say).
Regards,