Bug is reproducing 50 / 50. I tried to insert a 100ms delay into my worker routine. With this delay bug is not reproduced. I think, there is an interop with work thread which try to join to multicast ( tcpip!IppMulticastWorkerRoutine ). The main
problem is the callout driver failed HCK test "Winsock Core Functional Test" with reason: "The test logs show that all UDP multicast datagrams are being dropped for both IPv4 and IPv6 tests"