This is one of those things that you read once, say \"aha!\" and then forget. Exactly my case.
Why is the line-break tag in xhtml preferentially written with a space
is valid (old) HTML, while is not. If you are serving your XHTML as XML, it doesn't matter. If you are serving it as text/html, then it needs to be valid HTML in addition to being valid XHTML. (Why serve XHTML as HTML? Because IE doesn't understand XHTML as XML, and because no major browser will start rendering XHTML mid-way through downloading the text, but they will do that to HTML. My blog appears to load slowly not because the site is slow, but because the browser won't start rendering the page until everything has been fetched. I hate browsers.)