Current implementation of isActive() is:

    public boolean isActive()
    {
        boolean isActive = super.isActive();
        if( isActive )
        {
            //do not join transaction if org.jpox.Transaction already started
            return true;
        }
        joinTransaction();
        return isActive;
    }

The following fragment causes a
org.jpox.jdo.exceptions.TransactionNotActiveException on makePersistente() call

            PersistenceManager pm = pmf.getPersistenceManager();

            ut.setTransactionTimeout(300);
            ut.begin();
            Product product = new Product("Sony Discman", "A standard discman from Sony", 200.00);
            pm.makePersistent(product);


Using the debugger it is clear that if
        boolean isActive = super.isActive();
returns false, the active JTA transaction is correctly joined with the call to joinTransaction(); that
correctly toggles active flag to true in the superclass.
unfortunately local method variable isActive is not updated so the result is still false.