Backbone: Collection does not purge internal `_byId` reference to a removed model

Please find below about the tersest reproduction I could fathom of a sequence of steps in a Backbone application that leads to a Collection getting into a state of internal confusion.

A working copy can be found in this JSFiddle .

What it demonstrates is a collection keeping an internal (_byId) reference to a remove()-ed Model. That Model is no longer part of collection.models, however, it can still be retrieved through its (former) id.

var
    MyView = Backbone.View.extend( {

        initialize: function () {

            this.model = new Backbone.Model( {

                id:  'foo'
            ,   foo: 'bar'
            } );

            this.collection = new Backbone.Collection( this.model );

            this.listenTo( this.model, 'change:id', function ( model, id ) {

                if ( id == null ) {
                    this.collection.remove( model );
                }

            } );

            this.model.unset( 'id' );

            $('#models' ).val( JSON.stringify( this.collection.models      ));
            $('#_byId'  ).val( JSON.stringify( this.collection._byId       ));
            $('#get-foo').val( JSON.stringify( this.collection.get( 'foo' )));
        }

    })

, foo = new MyView()
;