- Given that I believe the problem only appears in Chrome on Windows, perhaps Chrome on Windows is the culprit, and that it isn't correctly honoring the FontFace rendering?
That would be my guess as well. We know that the problem is not linked to a specific font, and we know that the problem is not caused by Font Squirrel (since the issue is browser-specific).
You managed to work around the problem with the optgroup tag, but we can't include that tag into Jetpack Contact Forms without creating a new option to specify different option groups when using dropdowns in the form.
I opened #1770-plugins, and we'll consider adding optgroup in a future Jetpack release.
Thanks for your feedback!