1. Go to http://webkit.org/blog-files/3d-transforms/poster-circle.html
2. Drag the tab out of the Safari window
The mini-window you're dragging doesn't show any of the compositing layers.
This same problem is also making it impossible to get pixel results for tests that use compositing.
*** Bug 78439 has been marked as a duplicate of this bug. ***
We no longer ship Safari on Windows.