same named relationship from two subclasses cant be targeted

due to the path reduction. a simple switch to use non-reduce paths fails to even initiate the eagerload at all.

from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import *
from sqlalchemy.orm import relationship, subqueryload, Session

Base = declarative_base()

class A(Base):
    __tablename__ = 'a'
    id = Column(Integer, primary_key=True)
    type = Column(String)

    __mapper_args__ = {'polymorphic_on': type}

class B(A):
    __tablename__ = 'b'
    id = Column(Integer, ForeignKey('a.id'), primary_key=True)

    btod = Table('btod', Base.metadata,
        Column('bid', Integer, ForeignKey('b.id'), nullable=False),
        Column('did', Integer, ForeignKey('d.id'), nullable=False)
    )
    related = relationship("D", secondary=btod)
    __mapper_args__ = {'polymorphic_identity': 'b'}

class C(A):
    __tablename__ = 'c'
    id = Column(Integer, ForeignKey('a.id'), primary_key=True)
    ctod = Table('ctod', Base.metadata,
        Column('cid', Integer, ForeignKey('c.id'), nullable=False),
        Column('did', Integer, ForeignKey('d.id'), nullable=False)
    )
    related = relationship("D", secondary=ctod)
    __mapper_args__ = {'polymorphic_identity': 'c'}

class D(Base):
    __tablename__ = 'd'
    id = Column(Integer, primary_key=True)

engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = Session(engine)

d = D()
session.add_all([   B(related=[d](
)),
    C(related=[d](d))
])
session.commit()

for a in session.query(A).with_polymorphic('*').\
        options(subqueryload(B.related), subqueryload(C.related)):
    print a.related

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