This has been brought up many times. It depends on what font you are using. Different fonts display the control codes differently. Unfortunately, there isn't an easy way around that. There may be a change at some point that will resolve that, but it will probably be quite a while before it happens because of the difficulty in finding an option that works correctly. You will also notice this with Ctrl-I in some fonts, where it appears to put a TAB (multiple spaces) where the Ctrl-I is. Unless mIRC goes to a WYSIWYG script editor and command/edit line or uses an image for the control codes, I don't really expect to see it change.