Blocker Description
On our integration test clusters, while testing http://gerrit.sjc.cloudera.com:8080/#/c/5740/ we were able to reproduce a bug wherein one of the replicas inverted the order of two requests (an INSERT and later MUTATE of the same row). This caused the MUTATE to fail with a "Not Found" error and the replicas to diverge. After hours of staring at the code, I think I understand what's happening. Detailed explanation below...