Juha, thank you *** so much! ***
Our problem is now solved - we just added the localhost's actual IP address to the /etc/hosts file, and the problem went away.
The real cause of the problem was that the devel network doesn't run DNS, therefore had local net entries for when dsl goes down. Deploy net runs DNS therefore hadn't added entires.
This behaviour of JBoss is imho quite strange - I mean, why can't it use the DNS???
Should this be logged as a bug (feature?) on sourceforge?
Anyway, Juha, thanks again, you've saved me from much much pain!