We recently ran into an issue with web fonts disappearing from the font stack after switching a site over to use Amazon Cloudfront CDN.
With the Drupal CDN module set to 'Disabled', the fonts would appear as expected but when served from the CDN, the browser would fallback to the next font in the stack. The Net inspector showed the fonts were actually being downloaded from the CDN but just didn't appear. This was the case in recent versions of Firefox, Chrome and IE. Safari displayed the font properly.