Strange multicast behaviour...A bug?

[Russell Strong]

Today I observed that multicasting does not work without a default 
route.  Naturally I expected it to not get past the local subnet. 
However, I was surprised that I was not able to receive the traffic on 
the SAME host that was sending it.  Is that a bug?  Even if no one else 
is able to receive the join.  Why can't the joining host still join????

Russell