code: function getPendingBackingStore(instance) {
      var proto = Object.getPrototypeOf(instance);
      var pendingStores = proto._pendingBackingStores;
      var pending = core.arrayFirst(pendingStores, function (pending) {
        return pending.entity === instance;
      });
      if (pending) return pending.backingStore;
      var bs = {};
      pendingStores.push({ entity: instance, backingStore: bs });
      return bs;
    }
docs: workaround for IE9 bug where instance properties cannot be changed when executing a property 'set' method.