This is what I'm using...
<head>
{etc}
</head>
</html>
<body>
{etc}
</body>
Seriously?? There should be no <head>, <body>, or <html> tags in custom islands or headers/footers -- they're already embedded into each page. And the </html> tag in the middle??
I'm surprised it even works... unless Threads is stripping those tags (they aren't rendering on your site, so maybe that's the case?)...