sharding/SERVER-7379.js fails with a mixed version cluster

var config = {                                              

        mongos: 2,                                          

        shards: 2,                                          

        other: {                                            

            rs: true,                                      

            mongosOptions: { binVersion: "2.8"},       

            configOptions: { binVersion: oldVersion},       

            rsOptions: {binVersion: ["2.6"], nodes:3}

        }                                                                       

    };                                                      

assert.writeError(offerChange.update({ _id: 123 },                                   

                                     { _id: 123, categoryId: 9881, store: "NEWEST" },

                                     true, false));