> - but, I don't have a transaction that spans multiple databases at
> all; nor two-phase commit; nor subtransactions;

All transactions use two-phase commit. If you do not use JCA or XA
connections, prepare is followed by commit. However if you deploy JayBird as
RAR (firebirdsql.rar), it automatically means that XA transactions are used.

Now the question is how could it happen that JBoss did not commit the
prepared transaction...

Roman