it became apparent that i was making mistake on my test.  for me
	IPv6 linklocal multicast is working right, for multiple machines,
	with multiple flavors of interfaces.  i dunno what is happening.
	if you can check netstat -sn output and compare before and after the
	test, you may see something odd (like packets are not received at all,
	due to packet filters on ethernet cards).

itojun