And what you're describing is perfectly normal behavior, because it's got nothing to do with line spacing at all.
In most word processors you do not hit Enter to go to the next line, but to go to the next paragraph. As you've already observed Word will take care of single spacing the actual lines you are creating as you type them by wrapping when necessary and keeping single spacing,
If you want to make Word behave as though you're using a typewriter then you need to go into the Line and Paragraph spacing and either set the spacing after a paragraph to 0 pt and/or check the box that sets the "Don't add space between paragraphs of the same style" property.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
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