I would say that this is most definately a bug in JBossMQ. If you are a new bee to J2EE I can see it may be scary, but the CVS version of 2.4.1 should be much more stable.
Thank you Peter.
Yes, it is scary that a subscriber crashes after 40 seconds caused by a bug in the app-server. So 2.4 final is not recommended for production, I think.
I'll try the 2.4.1.
Or you can try the JBossMQ 1.0.0 Beta standalone server. It is MUCH better that what is in 2.4.0