All problems have been found. After instantiating two PropertyManagers, listening to VM states and tasks states at the same time creates an Unexpected block. The function beginwaitforupdates looks like the function waitforupdatesex, and two calls will cause thread be suspended.
And An error in the example, Codes in PropertyManager.cs lines 179, ((webclientasyncresult)_ Asyncresult). Abort(); in the stoplistening function causes an exception. Type cast failed. maybe should close the AsyncWaitHandle.
