I had your same experience, then I opened the syntax guide in another window and indented something four spaces, tried again. It rendered the very simple markdown as HTML.

Pretty good. I might show this to my friend who is trying to learn Javascript, doesn't know any HTML or Markdown now, probably will need to learn both, slightly interested in parsing and parse trees, but I don't know how useful it is.

I wouldn't put this on the front page though.

A small bug issue with firefox which is fixed now