This happens to me only when somebody has posted a really long url without "condensing" it by clicking on the "url" button during composition. Then the whole address or link just scrolls out horizontally, forcing the entire thread into that format! That's really annoying, and it's not just newbies who don't know how to post a link.

This may have nothing at all to do with the problem you're having, but it's the only time this happens to me. Hope this helps.