OK, so I ran a test. I took the Xara generated font, created my own html/css page with the embedded font - this reproduces the error:

.css (modified from Xara output):
Code:
@font-face {font-family: 'Poppins SemiBold';font-weight:normal;font-style:normal;src: url("XaraWDGeneratedHTMLfont2.woff") format("woff"), url("XaraWDEmbeddedHTMLfont2.eot?") format("embedded-opentype"), local('Poppins SemiBold'), local('PoppinsSemiBold');}

.xr_s32 {font-family:'Poppins SemiBold';font-weight:normal;font-style:normal;font-size:18px;}
.html

Code:
<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<link rel="stylesheet" href="stylesheet.css" type="text/css" charset="utf-8" />
<h1>My First Heading</h1>
<p class="xr_s32">My first paragraph.</p>

</body>
</html>
which gives:
Click image for larger version.  Name: Fontprob.png  Views: 68  Size: 6.3 KB  ID: 130928

So definitely seems to be an issue with the generated web font. Am I missing anything? Has anyone seen a solution to this somewhere?