The normal behavior of CSS is to cascade from parent to child, including vendor-prefixes. For some reason, the HTML button element is not able to received cascaded instances of the -webkit-font-smoothing property. If I manually set the element to include this property by a direct targeted class, element selector, etc. it works as expected. Please see this example: http://codepen.io/anon/pen/vckgG
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.