If you wiped mirc.ini and your settings are still there then you didn't wipe the right mirc.ini. Keep in mind 6.3 changes the directory which settings are loaded from by default, see the versions.txt
for info on that
20.For Vista compatibility, new installations of mIRC now save all
settings in the User's "Application Data\mIRC" folder by default.
However, if the installer or mIRC find mirc.ini in the same folder
as mirc.exe they will use the mirc.exe folder for all settings.
Users installing over an old version of mIRC should therefore see
no change in behaviour.
The installer is now also aware of administrator and standard user
accounts and installs mIRC accordingly.
Make sure you dont have an mirc.ini in there, or that if you do, you're editing that file, otherwise that's likely why your settings seemed to have "disappeared"