public void BUG__0002__BulkUpdateFailsWhenCalledFromMultipleThreads() { var col = new ObservableCollectionEx<int>(); var t1 = Task.Factory.StartNew(() => { using (col.BeginBulkUpdate()) { col.Add(1); Thread.Sleep(10); } }); using (col.BeginBulkUpdate()) { col.Clear(); } // code above would normally fail by now. }