"http://schema.org/Thing" and its descendants are no longer valid HTML. This seems to have been broken in Q1-Q2 2014, based on archived versions in the Internet Archive. In particular, the list of "More Specific Types" uses "li" items which are no longer within a "ul". (There's also an extra "/table" and a bogus "/span" tag in there.) This makes it harder to machine-process that data.

I assume those pages are automatically generated from "https://github.com/schemaorg/schemaorg/blob/master/data/schema.rdfa", which was new in 2014, so this is probably just a bad template.

W3C validation report: http://validator.w3.org/check?uri=http%3A%2F%2Fschema.org%2FThing&charset=%28detect+automatically%29&doctype=Inline&group=0