BR,
Your output HTML is very incorrect. The actual article text is surrounded by separate head and body tags. There should only be one grouping of html, head, and body tags on your site. More than that completely breaks HTML formatting and can cause numerous problems, including the one you mention.
If you open the HTML for your home page in your browser, you'll be able to see the following block of code toward the bottom:
<div class="art-postcontent">
<div class="art-article"><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head><head>
<link rel="shortcut icon" type="image/x-icon" href="/favicon.ico">
So, something in the art-postcontent div is trying to create a whole new web-page element within the page. That <html><head></head> tag and the closing tags for them at the bottom of the page need to be removed.
I have no idea what's causing that, but hopefully the above information gets you or your developer started on looking into the problem.
Thanks,
Alex