Comment 23 for bug 1080765

Taking a fresh look at this, I remembered having already dealt with this issue:

   # Requiring "AND master_crc IS NOT NULL" avoids a race condition
   # when the system is fast but replication is slow. In such cases,
   # we can select on the slave before the update for $update_sth
   # replicates; this causes a false-positive diff.
   my $sql = "SELECT MAX(chunk) FROM $repl_table "
           . "WHERE db='$tbl->{db}' AND tbl='$tbl->{tbl}' "
           . "AND master_crc IS NOT NULL";

That was put in in 2.0. So #1-#4 (comment #17) shouldn't be able to happen before #5. Maybe something else is wrong. I'm taking another look.