This post had a centered H2 header that appeared fine in the wysiwyg post editor during composition but is absent in the Preview or actual Post (in my firefox 3.6.6).
It appeared in the source view, during composition in the editor, like this,
<h2 style="text-align: center;">This my header.</h2>
I tried it also in an earlier submission, with the same result. When I attempt to re-edit that comment, the header was then missing in the source view as well as the posted view.
Could it be, that the submission step causes some html content to vanish?