I think it might be something to do with the size of the window that you view it in - I remember when I did mine I pasted it in on my laptop and it looked fine, then later I changed a bit using my mum's Ipad and the lines were all weird like you say. I think it's just to show what they're counting as a 'line' when you're viewing it in a smaller window where their version of a 'line' won't actually fit on a single row.
I might be wrong though!