> db.system.foo.insert({})
2014-02-03T16:09:53.434-0500 batch failed, cannot aggregate results: cannot write to 'test.system.foo' at src/mongo/shell/batch_api.js:612

> db.system___foo.insert({})
SingleWriteResult({
        "writeErrors" : [ ],
        "writeConcernErrors" : [ ],
        "nInserted" : 1,
        "nUpserted" : 0,
        "nUpdated" : 0,
        "nModified" : 0,
        "nRemoved" : 0,
        "upserted" : [ ]
})
> db.system___foo.renameCollection('system.foo')
{ "ok" : 1 }
> db.system.foo.find()
{ "_id" : ObjectId("52f005ae6d0abd019aead824") }