It looks to me that if -Djava.net.preferIPv4Stack property is not specified, JGroups prints out this warning and exception:

[JBoss] 05:57:35,544 WARN [UDP] could not bind to /234.1.78.86 (IPv4 address); make sure your mcast_addr is of the same type as the preferred IP stack (IPv4 or IPv6) by checking the value of the system properties java.net.preferIPv4Stack and java.net.preferIPv6Addresses.
[JBoss] Will ignore mcast_addr, but this may lead to cross talking (see http://www.jboss.com/wiki/Edit.jsp?page=CrossTalking for details).
[JBoss] Exception was: java.net.BindException: Cannot assign requested address