I'm not sure you're using the term "ASCII" correctly. There are virtually no characters in ASCII that aren't printed on a key on a typical US keyboard.
Especially when you say "with a font that has all the necessary characters". ASCII is ASCII. All fonts (except Wingdings) have 100% of the ASCII characters.
Maybe you're pasting in Unicode; maybe you're using the Windows-only ALT-numeric keypad garbage.
But I suspect your "nice formula" that renders in a text editor maybe isn't as clean or standard as you think.
Especially when you say "with a font that has all the necessary characters". ASCII is ASCII. All fonts (except Wingdings) have 100% of the ASCII characters.
Maybe you're pasting in Unicode; maybe you're using the Windows-only ALT-numeric keypad garbage.
But I suspect your "nice formula" that renders in a text editor maybe isn't as clean or standard as you think.