Question on encoding declaration check of HTML5 conformance checker

Hi all,

I used the HTML5 conformance checker on
http://validator.w3.org/check?uri=http%3A%2F%2Fwww.w3.org%2FTR%2Fhtml401%2Fstruct%2Fglobal.html&charset=%28detect+automatically%29&doctype=HTML5&group=0
which resulted in this error message:

"Internal encoding declaration iso-8859-1 disagrees with the actual encoding
of the document (utf-8)."

However, looking at the HTTP headers, the document is actually served as
iso-8859-1, so there is no clash to the "meta" element. Is there any
explanation for this error message I am missing?

Thanks,

Felix