I confirm the bug. It happens to every element that has font-family: sans-serif. I tested it with an html5 document, a version of your code:
Spoiler:
PHP Code:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Some title</title>
<style type="text/css">
p
{
font-family: sans-serif;
}
h1, h2, h3, h4
{
font-family: serif;
}
</style>
</head>
<body>
<h2>This headline should have a serif font.</h2>
<p>This paragraph should have a sans-serif font.</p>
</body>
</html>
Can you add your informations in the original post? Thanks
EDIT: ah, if I set both h2 and p with sans-serif, text is displayed as serif anyway, so it's not caused by the use of two different families.