I am experiencing this same issue as described here.
The topic was locked due to “cannot reproduce” so here is some more specific information.
play any video in this thread and go full screen
Chrome 51.0.2704.106 m
Works in Firefox
I have found that viewport size influences the bug.
on smaller screens the functionality works fine. on large screens the bug manifests itself.
I suspect it has to do with html elements overlapping the video player in certain responsive layout states.