Why HibernateTransactionManager create new session holder

While debugging, I encountered the following situation:

In Spring 5, class HibernateTransactionManager have code:

// ...
if (!txObject.hasSessionHolder() || txObject.getSessionHolder().isSynchronizedWithTransaction()) {
    Interceptor entityInterceptor = getEntityInterceptor();
    Session newSession = (entityInterceptor != null ?
                        obtainSessionFactory().withOptions().interceptor(entityInterceptor).openSession() :
                        obtainSessionFactory().openSession());
    txObject.setSession(newSession);
}
// ...

Why creating new session holder, if existing has isSynchronizedWithTransaction is true? As result, thread-bound session replaced with new session. It seems that the point of synchronization is to use the same session in a transaction, or do I understand it wrong?