In the test ManualTests/scrollbars/scrollbars-in-composited-layers.html, the box-shadow will become darker and darker when the scrollbar is used. This is due to a mismatch of what area of the tile is cleared and what is painting, since paintGraphicsLayerContents does not enforce clipping.
Created attachment 192938 [details] Patch
Comment on attachment 192938 [details] Patch Clearing flags on attachment: 192938 Committed r145803: <http://trac.webkit.org/changeset/145803>
All reviewed patches have been landed. Closing bug.