[Twisted-Python] Twisted: [twisted.internet.defer#critical] Unhandled error in Deferred:

Is it intentional to trigger this message? The reason I ask it it comes from defer.py DebugInfo.___del__(). I though that DebugInfo objects are only created if defer.DebugInfo.debug == True. But in Deferred._runCallbacks:701 its created without a check in the debug flag. The reason I have noticed is that during my app shutdown an ftp.FTPClient object is deleted that I think is causing the ftp connection to close and the connectionClosed event is not handled. Barry