Thanks for your bug report. I just tested this on several IRC networks and it seems to be working correctly. The /whois reply will contain the userid from your email address or from your identid, depending on whether you have "use id from email address" enabled or disabled.
If the server you are connecting to is not showing the correct userid, it may be that they are using your userid from the USERNAME logon, which uses your email address, instead of your identd userid. You can check to see what mIRC is sending to the server by using the /debug on command, which will output raw server messages to a debug.log file.
