Keep notifying changes for replaced objects

[bago]

var subModel = {
  c: ko.observable(1),
  d: ko.observable(0)
};

var subModelB = {
  e: ko.observable(0),
  f: ko.observable(1)
};

var model = {
  a: ko.observable(1),
  b: {
    g: ko.observable(0),
    h: ko.observable(0),
  },
  sub: ko.observable(subModel),
};

var w = ko.watch(model, { depth: -1, oldValues: 1, mutable: true, tagFields: true }, listener);

model.sub(subModelB);
subModel.c(4); // this is a change in a model being removed by the original tree, but still the listener is notified with this change.

Some "unwatch" is not working correctly.