I've just booted up Windows and I can confirm this is behaving very peculiarly. It seems to be totally ignoring the overflow: hidden CSS that we have here.
I compared it to other browsers, and there's no issue. I installed Chrome Canary (which is version 67 I believe) and the issue is gone. Therefore I suspect this will be fixed in an upcoming Chrome 65, 66 or 67 release, and there's nothing further for us to do at this stage.