I know the title was probably hard to explain so let me explain again here. Say your article was called How to Lose fat in 20 days. But in your <title> and slug, you use How to Lose Fat and how-to-lose-fat, since using less is better for search engines. Is this bad practice? They're basically both convey the same meaning. Can you get penalized for this by search engines?
No, you won't penalize for doing that. But for the sake of consistency, use the original title of the article.
Well I'll give you an example because I want to optimize my titles for readers, but want to optimize my <title> for search engines. For example: (visible title)Windows 7 and Windows XP Mode: Can you run it? But I want the <title> to be Can you run Windows XP Mode on Windows 7?
I do that very often, my titles are geared towards getting more clicks when my page appears in search results. Though content within 'h1' might be different.