Workaround for https://github.com/LearnBoost/mongoose/issues/423

gistfile1.js

Model.post('init', function() {
  if (!this.isNew) {
    var my = this
      , activePaths = Object.keys(this._activePaths.states.init);
    Object.keys(my._doc).forEach(function(path){
      if (activePaths.indexOf(path) === -1) {
        delete(my._doc[path]);
      }
    });
    this._doc = my._doc;
  }
});