Clicking fullscreen button breaks scrolling until page refresh

Steps to reproduce:

1. Visit http://www.youtube.com/html5 and make sure HTML5 video will be used
2. Visit http://www.youtube.com
3. Select a video
4. Press the "fullscreen" button in the bottom right of the video
5. Click back inside the main web frame outside of the video.
6. Observe that mouse wheel and arrow keys no longer function to scroll the page. Additionally, touch events do not work. (The touch case is the one I'm dealing with but I verified it's broken with mouse as well.)

Refreshing the page fixes the issue until the next occurrence.

This was done with a QML WebEngineView element. The WebEngine view does NOT implement a handler for onFullScreenRequested. When I do implement this handler and call request.accept(), the problem goes away. (However we do not want to do this in our use case.)