Consider the following multicast sequence :
 joinGroup(inetAddress) ;
 send(hi) ;
 leaveGroup(inetAddress) ;

Suppose that this code is execute in a thread and that the thread dies just after the leaveGroup method code.
With jdk 1.1.8, the sent message is never received.
With jdk 1.2.1 the sent message is received.

Code to reproduce the problem is put in attachment.