(function() {
    db.c.insert({a:1});
    db.c.insert({a:1});
    printjson(db.c.explain("allPlansExecution").distinct("a"));
})();

$ resmoke.py --suites=core repro-file.js

Currently nReturned will be 2 (rather than 1). If an index

is created, then nReturned will be the correct value of 1.

Once this is fixed, there may be special work we have to do to get this to work correctly under sharded clusters.