Are you using the sequence on multiple tables?
No, I don't.
In addition the sequence does not use the cache option.
Could a transaction rolling back be causing the gap?
No, it happens always, and is reproducible.
As the manipulation is purely within oracle you would need to examine the database interactions between JBoss AS and Oracle in order to discover any possible interaction which could lead to this behaviour.
Thank you for your reply.
Do you know what I could use to analyze the interaction between Oracle and JBoss AS?