Hi, the example code returns true for session.isDirty (as expected) but no sql will be executed.

try {
tx = session.beginTransaction ();

// creating a many-to-many for two persistent entities

System.out.println(session.isDirty ());
tx.commit ();
}
catch (Exception e) {
if (tx != null) {
tx.rollback ();
}
}
finally {
session.close ();
}

Are there any know conditions for that behaviour, or do I misinterpret the api doc?
Hibernate version is 3.1.3

Have you logged any exceptions? If isDirty returned true but an exception was thrown before any SQL was generated, that would explain what you're seeing.

Adding an element to a set makes the session dirty even if the element was in the set already.