Simple test

DataSource dataSource = (DataSource) PortableRemoteObject.narrow(
jndi.lookup("java:/SomeDS", DataSource.class);
Connection conn = dataSource.getConnection();

conn.setTransactionIsolation(Connection.TRANSACTION_REPEATABLE_READ);

Here you get exception that there is no transaction started on this
connection. The problem is that this exception is raised from
InternalCommit becouse InTransaction actually returns true.

Doychin