We've had a couple of tests fail recently in core suites on debug buildbots due to an (incorrect) second application of an update operation to a document. I haven't really investigated, but one possibility is that they are somehow related to the new, randomly triggered page fault exceptions in dev mode.

<http://buildbot.mongodb.org/builders/Linux%2032-bit%20debug/builds/1177/steps/test/logs/stdio>
<http://buildbot.mongodb.org/builders/Linux%2032-bit%20debug/builds/1183/steps/test/logs/stdio>