Validator Results give warning when there is none

I'm guessing this is an offshoot of the HTML5 validator not being finalized but it gives me a warning without anything (except the "Using experimental feature" notice) below. Shouldn't that show up as a notice in the results section above, or even not show up at all? It's the only thing ruining the HTML5 validation on the site I was working on (theamm.org)

NOTE: Whenever possible, give the address of the document you were checking.