One long outstanding bug of JBoss is that on a transaction timeout, that transaction is only marked for a rollback and not actually rolled back. This responsibility is delegated to the invocation thread. This can cause major problems if the invocation thread hangs indefinitely since things like entity bean locks will never be released. The solution to this problem is not a good one. You really just need to avoid doing stuff within a transaction that could hang indefinitely. One common mistake is making connections across the internet or running a web-crawler within a transaction.