If you open fast/layers/no-clipping-overflow-hidden-added-after-transform.html in Safari with tiled drawing, the green div doesn't show up. Seems to be some sort of z-ordering issue; if you translate it upward in Z it appears and the test works correctly. I'm going to mark it as failing in the patch in bug 121859, but this seems like an actual flaw with tiled drawing vs. just an issue with the test.
The test passes now, closing. http://trac.webkit.org/changeset/167362