http://trac.webkit.org/changeset/109008 introduced some changes to the lastIndex property in JSC. I suspect that the V8 bindings probably need to be updated to behave similarly, but don't understand enough about this problem to know what needs to be done. See: http://test-results.appspot.com/dashboards/flakiness_dashboard.html#showExpectations=true&tests=fast%2Fregex%2Flastindex.html
(In reply to comment #0) > http://trac.webkit.org/changeset/109008 introduced some changes to the lastIndex property in JSC. I suspect that the V8 bindings probably need to be updated to behave similarly, but don't understand enough about this problem to know what needs to be done. Correct me if I am wrong: I guess that this is not a problem of V8 DOM bindings but a problem of V8 itself (outside WebKit). It appears the properties of regular expressions are handled inside V8.
Filed here: http://code.google.com/p/v8/issues/detail?id=1976