Follow up:
While I’m pretty sure I duplicated this problem in Firefox, the consensus at WP and other web sources says it is a Chrome 45 issue, and to find this option in chrome:
chrome://flags/#disable-slimming-paint
And check the “enable” (that’s right: enable the disable option – a bit twisted….) I had to use the browser page serach to find that option: Disable Slimming Paint