The "Encodings support" page for libxml2 is valid XHTML 1.0 Transitional with an XML header that specifies the encoding as "ISO-8859-1", a <meta http-equiv> element that sets the Content-Type to "text/html" and the charset to "ISO-8859-1", served with HTTP headers that set the Content-Type to "text/html" and the charset to "UTF-8".
For some reason Because HTTP headers take precedence (see comments below) browsers decide that the page is UTF-8 and break the ISO-8859-1-encoded characters within it.