TinyMCE + forum not displaying correctly

The new WYSIWYG editor (TinyMCE) displays a format that the form does not render.

See this post with all the possible configurations, how they are rendered: JudgeApps | Log In

What I expected to see:

Heading 3 essentially being hidden is the most problematic:

H3 {
  POSITION: absolute;
  DISPLAY: block;
  OVERFLOW: hidden;
  WIDTH: 1em;
  LEFT: -999em;
}