assets/js/vendor/backbone-relational.js
function( model, coll, options ) {
			if ( ( this.keyId || this.keyId === 0 ) && model.id === this.keyId ) { // since 0 can be a valid `id` as well
				this.addRelated( model, options );
				this.keyId = null;
			}
		}
function( model, coll, options ) {
			if ( ( this.keyId || this.keyId === 0 ) && model.id === this.keyId ) { // since 0 can be a valid `id` as well
				this.addRelated( model, options );
				this.keyId = null;
			}
		}
If a new 'this.relatedModel' appears in the 'store', try to match it to the last set 'keyContents'