SqlAlchemy Relationship on Joined Inheritance fields Results in "where false" SELECT Statement - python-3.x

Question

If I have a shipment with a relationship shipment_legs, I expect that I can call
shipment.shipment_legs to gather all the legs from across the various tables. But the SQL Statement that I see when looking at the echo has an "AND false" appended to it
SELECT *
FROM container_shipment_leg
LEFT OUTER JOIN container_ocean_leg ON container_shipment_leg.id = container_ocean_leg.id
LEFT OUTER JOIN container_road_leg ON container_shipment_leg.id = container_road_leg.id
LEFT OUTER JOIN container_rail_leg ON container_shipment_leg.id = container_rail_leg.id
WHERE container_shipment_leg.shipment_id IN (3) AND false
# Models
class ContainerShipmentLeg(IDomainModel, ABC):
_leg_class: LegClass
sequence: int
def __init__(self, class_type: LegClass, sequence: int):
self._leg_class = class_type
self.sequence = sequence
#hybrid_property
def class_type(self):
raise NotImplementedError("Class Type must be implemented by Subclasses")
class ContainerOceanLeg(ContainerShipmentLeg):
vessel_name: str
voyage_number: str
#hybrid_property
def class_type(self):
return LegClass.SEA
def __init__(self, sequence: int):
super().__init__(self.class_type, sequence)
class ContainerRoadLeg(ContainerShipmentLeg):
reservation_id: str
#hybrid_property
def class_type(self):
return LegClass.ROAD
def __init__(self, sequence: int):
super().__init__(self.class_type, sequence)
class ContainerRailLeg(ContainerShipmentLeg):
pickup_number: str
#hybrid_property
def class_type(self):
return LegClass.RAIL
def __init__(self, sequence: int):
super().__init__(self.class_type, sequence)
# Table
container_shipment_leg_table = Table(
"container_shipment_leg",
metadata,
Column("id", BIGINT, autoincrement=True, primary_key=True, key="id"),
Column(
"shipment_id",
BIGINT,
ForeignKey("shipment.id", link_to_name=True),
key="shipment_id",
index=True,
),
Column("leg_class", Enum(LegClass), key="_leg_class", nullable=False, index=True),
Column("sequence", INT, key="sequence", nullable=False),
)
container_ocean_leg_table = Table(
"container_ocean_leg",
metadata,
Column("id", BIGINT, ForeignKey("container_shipment_leg.id", link_to_name=True), key="id", primary_key=True),
Column("vessel", VARCHAR(50), key="vessel_name"),
Column("voyage_number", VARCHAR(50), key="voyage_number"),
)
container_road_leg_table = Table(
"container_road_leg",
metadata,
Column("id", BIGINT, ForeignKey("container_shipment_leg.id", link_to_name=True), key="id", primary_key=True),
Column("reservation_id", VARCHAR(30), key="reservation_id"),
)
container_rail_leg_table = Table(
"container_rail_leg",
metadata,
Column("id", BIGINT, ForeignKey("container_shipment_leg.id", link_to_name=True), key="id", primary_key=True),
Column("pickup_number", VARCHAR(30), key="pickup_number"),
)
# Mappers
mapper(
ContainerShipmentLeg,
container_shipment_leg_table,
polymorphic_on=container_shipment_leg_table.c._leg_class,
with_polymorphic="*",
)
mapper(
ContainerOceanLeg,
container_ocean_leg_table,
inherits=ContainerShipmentLeg,
polymorphic_load="inline",
polymorphic_identity=LegClass.SEA,
)
mapper(
ContainerRoadLeg,
container_road_leg_table,
inherits=ContainerShipmentLeg,
polymorphic_load="inline",
polymorphic_identity=LegClass.ROAD,
)
mapper(
ContainerRailLeg,
container_rail_leg_table,
inherits=ContainerShipmentLeg,
polymorphic_load="inline",
polymorphic_identity=LegClass.RAIL,
)
mapper(
Shipment,
shipment_table,
properties={
"shipment_legs": relationship(
ContainerShipmentLeg,
lazy=BULK,
single_parent=True,
backref="shipment",
)
},
)
I could use some help figuring out where the "And false" is coming from. INSERTING via the relationship seems to work fine