SourceForge Submitter: koreth .
If I bring up the stock 4.0.1RC1 distribution on a pair
of Linux systems (Debian sarge, Blackdown Java 1.4.2),
unmodified config files except adding a jvmRoute to
each system's Tomcat server.xml, I get a steady stream
of messages like

12:43:05,914 WARN [UDP] discarded message from
different group (Tomcat-Cluster). Sender was sgrimm2:32788
12:43:05,949 WARN [UDP] discarded message from
different group (DefaultPartition). Sender was
sgrimm2:32785 (additional data: 13 bytes)

The most likely cause is that both the Tomcat-Cluster
and DefaultPartition sockets are listening to the same
multicast address and port number, but they don't know
about each other.

Changing either service's multicast port number makes
the messages go away and, presumably, is a slight
performance boost since neither service's JGroups stack
has to deal with the other's messages.

It's entirely possible that these warnings are
harmless, but it sure doesn't look good to have the
default configuration spew warning messages that look
like they indicate dropped data.