assets/js/vendor/backbone-relational.js
function() {
			this.stopListening();

			if ( this instanceof Backbone.HasOne ) {
				this.setRelated( null );
			}
			else if ( this instanceof Backbone.HasMany ) {
				this.setRelated( this._prepareCollection() );
			}

			_.each( this.getReverseRelations(), function( relation ) {
				relation.removeRelated( this.instance );
			}, this );
		}
function() {
			this.stopListening();

			if ( this instanceof Backbone.HasOne ) {
				this.setRelated( null );
			}
			else if ( this instanceof Backbone.HasMany ) {
				this.setRelated( this._prepareCollection() );
			}

			_.each( this.getReverseRelations(), function( relation ) {
				relation.removeRelated( this.instance );
			}, this );
		}
When `this.instance` is destroyed, cleanup our relations.
Get reverse relation, call removeRelated on each.