See http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK2%20(Tests)/r138696%20(5398)/results.html for example. fast/css/sticky/inline-sticky-abspos-child.html, fast/css/sticky/inline-sticky.html, and fast/css/sticky/sticky-both-sides.html are failing here. You look look at http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20-%20webkit.org&tests=fast%2Fcss%2Fsticky%2Finline-sticky-abspos-child.html%2Cfast%2Fcss%2Fsticky%2Finline-sticky.html, you see that these tests are always or intermittently failing.
This doesn't appear to happen on bots any more. Will remove expectations.