Just for reference, are you running Windows at all? I'm wondering if it's only appearing under Chrome on Windows (which is where I'm seeing it).
I use a Mac, so the problem might indeed be OS-depended, which would make sense since it's related to fonts.
What happens when you remove your hacks to the contact form file, and try to customize the look of the form with another font, either with font-face or with a web safe font? Do you experience similar issues?