I've been trying to calculate a new article based on an original article and diffs.
http://en.wikipedia.org/w/index.php?title=Florida&diff=582177432&oldid=581998623 That is the diff table for certain revisions for the Florida Wikipedia page.
http://en.wikipedia.org/w/index.php?title=Florida&action=edit&oldid=581998623 That is the page source being used for the base article being diffed to.
http://en.wikipedia.org/w/index.php?title=Florida&action=edit&oldid=582177432 That is the page source of the next revision that the article is being diffed
If you open up these two sources in a text editor you can see the line count. Now, look at the diff table (first thing I linked). Look at the entry for the diff for original article line 359 and new article line 361. The lines before the change should line up, right? If I had to guess what's causing it, I would say it's the diffs above it. Part of a line is being removed, but not otherwise changed, and this removed text is then being added as a new paragraph.