Use the attached test case which relies on LayoutTests/media/content/counting.mp4. When you hover the mouse under the rectangle with the green border, the second region in the chain, the controls are displayed in a wrong position wrt to the video element.
Created attachment 228277 [details]
This is caused by the same problem at https://bugs.webkit.org/show_bug.cgi?id=132243 . Closing.
*** This bug has been marked as a duplicate of bug 132243 ***