var t = db.upsert_bad_index;
t.drop();
t.ensureIndex({a: 1, b: 1});
var res = t.save({_id: 1, a: [1, 2, 3], b: [4, 5, 6]});
printjson(res);
printjson(t.validate().keysPerIndex)
assert.eq(0, t.find().itcount());