[Sqlalchemy-tickets] Issue #3958: Sqlalchemy 1.1 doesn't remove duplicate rows in some cases while 1.0 does (zzzeek/sqlalchemy)

[anti-social <iss...@bi...>]

New issue 3958: Sqlalchemy 1.1 doesn't remove duplicate rows in some cases while 1.0 does
https://bitbucket.org/zzzeek/sqlalchemy/issues/3958/sqlalchemy-11-doesnt-remove-duplicate-rows

anti-social:

After the [commit](https://bitbucket.org/zzzeek/sqlalchemy/commits/ceeb033054f09db3eccbde3fad1941ec42919a54) next test case begun to fail:


```
#!python

class FilterUniqueJoinTest(fixtures.MappedTest, AssertsCompiledSQL):
    run_setup_mappers = 'once'

    @classmethod
    def define_tables(cls, metadata):
        Table('users', metadata,
              Column('id', Integer, primary_key=True,
                     test_needs_autoincrement=True),
              Column('name', String(50)),
              Column('date_created', DateTime, default=datetime.datetime.now))

        Table('orders', metadata,
              Column('id', Integer, primary_key=True,
                     test_needs_autoincrement=True),
              Column('user_id', Integer, ForeignKey('users.id')))

    @classmethod
    def setup_classes(cls):
        users = cls.tables.users
        orders = cls.tables.orders

        class User(cls.Comparable):
            pass

        class Order(cls.Comparable):
            pass

        mapper(User, users, properties={
            'orders': relationship(Order, order_by=users.c.id.desc())
        })

        mapper(Order, orders)

    @classmethod
    def insert_data(cls):
        User = cls.classes.User
        Order = cls.classes.Order

        sess = create_session()
        o1 = Order()
        o2 = Order()
        o3 = Order()

        u1 = User(name='Mike')
        u1.orders = [o1, o2]
        u2 = User(name='John')
        u2.orders = [o3]

        sess.add(u1)
        sess.add(u2)
        sess.flush()
        sess.close()

    def test_filter_unique_column(self):
        User = self.classes.User

        sess = create_session()

        users = (
            sess.query(
                User.date_created.label('dt'),
                User,
            )
            .options(joinedload(User.orders))
            .all()
        )
        assert len(users) == 2

    def test_filter_unique_func_column(self):
        User = self.classes.User

        sess = create_session()

        users = (
            sess.query(
                func.date(User.date_created, 'start of month').label('month'),
                User,
            )
            .options(joinedload(User.orders))
            .all()
        )
        assert len(users) == 2

```

Sqlalchemy 1.0:

```
#!text

test/orm/test_joins.py::FilterUniqueJoinTest::test_filter_unique_column PASSED
test/orm/test_joins.py::FilterUniqueJoinTest::test_filter_unique_func_column PASSED
```

Sqlalchemy 1.1:

```
#!text
test/orm/test_joins.py::FilterUniqueJoinTest::test_filter_unique_column PASSED
test/orm/test_joins.py::FilterUniqueJoinTest::test_filter_unique_func_column FAILED

```

Is it expected behaviour?