The question arose because you said
I copied the entire content of the post from the 'text' window an fed it to the wc3 validator,
That suggested that your site might be only on your local computer -- because that's a way of validating for sites that are not accessible on the internet.
Copying only rendered HTML for a post won't rule out all possible coding problems that may be affecting a post. More effective to use the URL of the page in the validator to validate the entire page -- and that way you won't get the missing DOCTYPE problem (assuming you have one -- Andrew raised that question because sometimes people on self-hosted sites muck things up so badly that they have no DOCTYPE and that wreaks havoc with some browsers).
But now that you've posted the URL, this all becomes somewhat moot, as your site is on WordPress.COM. These forums are for self-hosted WordPress.ORG sites, so you'll need to post on the WP.COM forums for help with this. I did look at your page, but did not see anything obviously wrong, so hopefully someone on .COM can shed some light on it.
Sorry for any confusion here on my end...