Sqlalchemy complains that foreign key doesn't exist but actually it exists

I have the following models:

class Look(Base):
  __tablename__ = "looks"
  id = Column(Integer, primary_key=True)
  url = Column(String, nullable=False, unique=True)

class Similarity(Base):
  __tablename__ = 'similarities'
  __table_args__ = (UniqueConstraint('look_id_small', 'look_id_big'),)
  id = Column(Integer, primary_key=True)
  look_id_small = Column(Integer, ForeignKey('looks.id'), nullable=False)
  look_id_big = Column(Integer, ForeignKey('looks.id'), nullable=False)

When I am running this code:

try:
  with session.begin_nested():
    similarity = Similarity()
    similarity.look_id_small, similarity.look_id_big = look_id1, look_id2
    session.add(similarity)
    session.commit()
except Exception, e:
  logging.error(e)
  print "look_id1: %s, look_id2: %s" % (look_id1, look_id2)

This is the error I am getting:

2013-01-19 04:55:42,974 ERROR Foreign key associated with column 'similarities.look_id_small' could not find table 'looks' with which to generate a foreign key to target column 'id'
look_id1: 217137, look_id2: 283579

so I tried looking for these values in pgsql and they do exist!

giordano=# SELECT * FROM looks WHERE id = 217137 or id = 283579;
   id   |                      url                      | title | image_url | 
--------+-----------------------------------------------+-------+-----------+
 217137 | http://foo.com                                |       |           |     
 283579 | http://baz.com                                |       |           |
(2 rows)

I have spent the whole night trying to figure this out.

Some clues:

1. I am only getting these errors on certain values.
2. I don't think having double foreignkeys on the same table will result in an issue.

Anyone?

EDIT:

giordano=# \d+ looks