MulticastSocket.setInterface(InetAddress) simply sets the socket option IP_MULTICAST_IF. This interface value is then used when joining/leaving a group as the in_addr for ip_mreq.imr_interface. The problem is that the address returned from getsockopt is not the same as the one used in setsockopt.

This is a native vista issue and can be reproduced with a simple native testcase (attached, TestIP_MULTICAST_IF.c). This needs to be fixed in the vista platform.
 Native Tests show:
  T:\6358574>TestIP_MULTICAST_IF
    Set IP_MULTICAST_IF = 129.156.232.46
    Get IP_MULTICAST_IF = 10.0.0.0

This causes the following jck tests to fail:
  api/java_net/MulticastSocket/descriptions.html#send
  api/java_net/MulticastSocket/descriptions.html#setTimeToLive[MulticastSocket1021]
  api/java_net/MulticastSocket/descriptions.html#setTimeToLive[MulticastSocket1022]
  api/java_net/MulticastSocket/descriptions.html#setTTL[MulticastSocket1018]
  api/java_net/MulticastSocket/descriptions.html#setTTL[MulticastSocket1019]