See for example <http://build.webkit.org/results/Apple%20MountainLion%20Debug%20WK1%20(Tests)/r127762%20(588)/fast/events/invalid-001-crash-log.txt>. Presumably AlternativeTextController’s timer is set by an earlier test and not cleared before this test runs.
fast/events/keypress-insert-tab.html asserts here too.
Mac code assumes that this is always on, yet there are editing tests that turn it off (and no code in the test runner to turn it back on after the test is over).
*** This bug has been marked as a duplicate of bug 82761 ***