On the page in the URL, make the window short enough so that when you scroll up, the video overlaps the position:fixed bar at the bottom. Note that it's possible to get into a state where the video can overlap the position:fixed bar. Resizing the window fixes it.
The issue here is that we're not doing layout on scroll, so we're not running the overlap logic in RenderLayerCompositor::computeCompositingRequirements().
Also seen on nyt.com, and in NetNewsWire themes.
Created attachment 47574 [details]