assets/js/vendor/backbone-relational.js
function( model, coll, options ) {
			//console.debug('handleRemoval called; args=%o', arguments);
			options = options ? _.clone( options ) : {};
			this.changed = true;

			_.each( this.getReverseRelations( model ), function( relation ) {
				relation.removeRelated( this.instance, null, options );
			}, this );

			var dit = this;
			!options.silent && Backbone.Relational.eventQueue.add( function() {
				 dit.instance.trigger( 'remove:' + dit.key, model, dit.related, options );
			});
		}
function( model, coll, options ) {
			//console.debug('handleRemoval called; args=%o', arguments);
			options = options ? _.clone( options ) : {};
			this.changed = true;

			_.each( this.getReverseRelations( model ), function( relation ) {
				relation.removeRelated( this.instance, null, options );
			}, this );

			var dit = this;
			!options.silent && Backbone.Relational.eventQueue.add( function() {
				 dit.instance.trigger( 'remove:' + dit.key, model, dit.related, options );
			});
		}
When a model is removed from a 'HasMany', trigger 'remove' on 'this.instance' and notify reverse relations.
(should be 'HasOne', which should be nullified)