I forgot: we are using JBoss 4.0.4
Might there be a bug in the JGroups implementation which causes this strange behaviour?
If you can create a test case that shows your issue w/o use of JMX console (i.e. code the test to access the MBeanServer), attach it to a JIRA and I'll take a look.
we have solved the problem for us now. We've been trying different combinations of JBoss and JGroups, and found that it works in the combination of JBoss 4.0.4 and JGroups 2.2.9. Alternatively, what also seems to work is JBoss 4.0.5 and JGroups 2.4. So I assume it is a bug in JGroups 2.2.7, which shipped with JBoss 4.0.4.