Just done that, and this is interesting.
I took the same few paragraphs of text and posted them in three different fields - teaser paragraph, body and exclusive content.
Looking at the source all three were the same. When I posted the article, the first and third fields showed the double line spacing, the middle one (body) showed it the way it should be.
When I checked the source again, they're still showing the same.
Edit: I copied from an external text document and not from an already published article on my site. I will try again doing that.