It's the combination of border-radius + transparent border + subpixel position. <rdar://problem/17529112>
Created attachment 234415 [details] Test reduction non-retina only.
Created attachment 234418 [details] Patch
Comment on attachment 234418 [details] Patch Attachment 234418 [details] did not pass mac-wk2-ews (mac-wk2): Output: http://webkit-queues.appspot.com/results/5846429885005824 New failing tests: fast/borders/border-radius-on-subpixel-position-non-hidpi.html media/media-fragments/TC0001.html
Created attachment 234422 [details] Archive of layout-test-results from webkit-ews-16 for mac-mountainlion-wk2 The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews. Bot: webkit-ews-16 Port: mac-mountainlion-wk2 Platform: Mac OS X 10.8.5
Created attachment 234426 [details] Patch
Comment on attachment 234426 [details] Patch EWS testing.
Comment on attachment 234426 [details] Patch Clearing flags on attachment: 234426 Committed r170817: <http://trac.webkit.org/changeset/170817>
All reviewed patches have been landed. Closing bug.
The test is failing: http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK2%20(Tests)/r170843%20(18330)/results.html
(In reply to comment #9) > The test is failing: > http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK2%20(Tests)/r170843%20(18330)/results.html http://trac.webkit.org/changeset/170846