When you copy a line or the whole paragraph and paste it at another spot, you're also bringing with that line, some aspects or hidden codes of the original post.
Nope, not the case. Cheetah just catches the fact that the content of your post is duplicated elsewhere on the internet. If you've copied something with tags and meta data, you can always paste it in notepad and then copy it from there and it would just clean text since notepad doesn't preserve anything else but the visible text. But that's not going to help you with Cheetah at all.
I personally think Cheetah is extremely annoying when people are reposting their own content that they have used somewhere else (like their own blog) but besides that caveat, is pretty useful in seeing people that are stealing other people's work and passing it off as their own as those don't deserve our upvotes.