Code was updated to use <h3> while the (cached) skin CSS still had <h5>
See
http://lists.wikimedia.org/pipermail/wikitech-ambassadors/2012-November/000…
Note: code was reverted to wmf4, so the problem will appear now in the
reverse.
We should use an intermediate CSS with rules appliying to portlets no
matter if they are h3 or h5. Then migrate again in a few days.