mongoose: Dynamically adding fields in the schema doesn't permit to add fields as usual

Hi,

When I dynamically add a field to a schema and instantiate it to a model, mongoose is not aware of any change made on this new field when I call save.

var schema = new mongoose.Schema({
  name: String,
  firstname: String
});

var person = db.model('persons', schema);
var a = new person();
a.name = "John";
a.firstname = "Doh";

a.save(function(err, savedGuy) {

  schema.add({
    field1: String
  });
  // schema is now updated with the field1
  var personV2 = db.model('persons', schema);

  personV2.findById(savedGuy['_id'], function(err, john) {

    // won't work
    john.field1 = 'Custom field 1 value';
    // will work
    john.set ('field1', 'Custom field 1 value');

    });
});

I create dynamic but persistent schemas in my project. I can’t fill any data until I restart node. It looks like a bug for me. The purpose of schema.add function should be to avoid the use of set() which seems useful only for arrays properties that can’t be detected by mongoose.

I need right now to intensively manipulating objects which is not pretty at all. So my questions are : is this an issue ? If so, is this possible to think about a fix ?

Best regards and thank you for your work !