Compare two Ember objects (created with Ember.Object.create method)

I created a custom object with the Comparable mixin and added it to a model as an attribute with Ember transforms

var customObject = Ember.Object.extend(Ember.Comparable, {
    compare: function() {
        debugger;
    }
});  

Once the model is ready I create a copy of the custom object and add it as an attribute to the so that I can compare the custom object when it changes to this original value

export default DS.Model.extend({
    custom: DS.attr("custom-object"),

    ready: function() {
        this.set("originalCustom", Ember.Object.create(this.get("custom")));
    },

    isUpdated: function() {
        return Ember.compare(this.get("custom"), this.get("originalCustom"));
    }
});  

I manually call isUpdated to check if the compare method is invoked, but it never gets hit.
What am I missing here?