reIndex command ignores writeConcern

Using an older version of the shell (one that doesn't use OP_COMMAND?): rs:PRIMARY> db.test.find() { "_id" : 1 } rs:PRIMARY> db.test.getIndexes() [ { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.test" } ] rs:PRIMARY> db.runCommand({ reIndex : "test", writeConcern : { w : 9 } }) { "nIndexesWas" : 1, "nIndexes" : 1, "indexes" : [ { "v" : 2, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.test" } ], "ok" : 1 // <=== the test was expecting an error back from the server } rs:PRIMARY>