Objects onChange function not getting called when property is set from another object's setter function

[Appsolute-ly]

I have a parent and child object that are setup to be watched separately. In the parent object, I have a getter and setter to expose access to a property on the child. I've noticed that the onChange function does not get called for the child object when calling the setter on the parent object. I've set up a basic example to reproduce this problem here.