1. Make sure you are using the default Fixedsys font.
2. Then:
//echo -a $str($chr(7),100)
It will produce a line of dots. Highlight that line with your mouse, So as to copy the text. You should see the distortion.
This also happens with other characters in the FixedSys font.
I don't know if it happens for other Fonts.
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Found with XP Pro, mIRC 6.14.