unnecessary lazy loading of backref attribute

this test

class TestBackrefLoad(AssertMixin):
    def setUpAll(self):
        global metadata
        metadata = MetaData(testbase.db)
        self.a_table = Table("a", metadata,
                Column("id", Integer(), primary_key=True),
                Column("name", String()),
            )
        self.a_table.create()
        self.b_table = Table("b", metadata,
                Column("id", Integer(), primary_key=True),
                Column("a_id", Integer(), ForeignKey("a.id"))
            )
        self.b_table.create()
    def tearDownAll(self):
        self.b_table.drop()
        self.a_table.drop()

    def testbasic(self):
        class A(object):
            def __init__(self,id):
                self.id = id

        class B(object):
            def __init__(self,id):
                self.id = id

        mapper(B,self.b_table,always_refresh = True)
        mapper(A, self.a_table, properties={
            'b_list': relation(B,private=True,backref = 'a_link')},always_refresh = True)
        #First, populate some data
        sess= create_session()
        a= A(1)
        sess.save(a)
        a.name = 'test'
        b = B(10)
        sess.save(b)
        a.b_list.append(b)
        sess.flush()
        sess.close()

        #Now, get instance and change it name
        sess1 = create_session()
        a = sess1.query(A).get(1)
        a.name = 'test2'

        c = a.b_list[0](0).a_link#Lazy loading a_link will change a.name to 'test'
        assert a.name == 'test2'
        sess1.close

shows what getting backref attribute will fire lazy loading operation and interferes with session editing.

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