serializing a Dictionary<string,object> in ProtoBuf-net fails

(NOTE: Dictionary where T is some ProtoContract / ProtoMembered class works fine. ) This issue only happened for me with type object.

I was trying to serialize a dictionary of Dictionary working.

typeof(object) doesn't work. Should it? Should I implement a string based work around?

In this scenario, object will only ever be a .net primitive.

    [Test]
    public void De_SerializeObjectDictionary2()
    {
        var d = new Dictionary<string, object>();

        d.Add("abc", 12);

        var ms = new MemoryStream();

        var model = ProtoBuf.Meta.RuntimeTypeModel.Default;
        //model.AutoAddMissingTypes = true;
        //model.AutoCompile = true;
        //model.InferTagFromNameDefault = true;
        //model.Add(typeof (object), false);
        //model.Add(typeof(Int32), true);
        //model[typeof (object)].AddSubType(50, typeof (Int32));

        model.Serialize(ms, d);
        Serializer.Serialize<Dictionary<string,object>>(ms, d);
        // <--- No serializer defined for type: System.Object

        // or
        //model.Add(typeof (object), false);
        //Serializer.Serialize<Dictionary<string, object>>(ms, d);
        //<-- Unexpected sub-type: System.Int32
        ms.Position = 0;

        var d2 = Serializer.Deserialize<Dictionary<string, object>>(ms);
    }

I attempted to define these types ahead of time... but I think they're handled by default by protobuf-net

        //model.Add(typeof (object), false);
        //model[typeof (object)].AddSubType(50, typeof (Int32));
        /*
        //model.Add(typeof(int), false);
        //model.Add(typeof(string), false);
        //model.Add(typeof(short), false);
        //model.Add(typeof(DateTime), false);
        //model.Add(typeof(long), false);
        //model.Add(typeof(bool), false);
        //model.Add(typeof(int[]), false);
        //model.Add(typeof(string[]), false);
        //model.Add(typeof(short[]), false);
        //model.Add(typeof(DateTime[]), false);
        //model.Add(typeof(long[]), false);
        //model.Add(typeof(bool[]), false);

        //model.Add(typeof(int?), false);
        //model.Add(typeof(short?), false);
        //model.Add(typeof(DateTime?), false);
        //model.Add(typeof(long?), false);
        //model.Add(typeof(bool?), false);
        //model.Add(typeof(int?[]), false);
        //model.Add(typeof(short?[]), false);
        //model.Add(typeof(DateTime?[]), false);
        //model.Add(typeof(long?[]), false);
        //model.Add(typeof(bool?[]), false);

        //model.Add(typeof(byte[]), false);
        //model.Add(typeof(byte), false);