When you preview a post with new text written underneath a block of text in quotes, an extra newline is added that does not show up in the final post.

Example: http://i26.tinypic.com/kcj9yr.jpg

This is a minor issue, but still an example of previews not matching what's shown in the final post. Almost seems like the closing quote tag terminates a line, in the preview? That would explain it.