[web2py] how to remove duplicate tables in smartgrid?

[Jim Gregory]

I am creating an application that has a one-to-many table that
references the same table twice:

db.define_table('product',
    Field('title', required=True, unique=True),
    Field('sku', required = True, unique=True),
    Field('description', 'text'),
    format = '%(title)s'
    )

db.define_table('related_product',
    Field('product_id', db.product, writable=False),
    Field('product', 'reference product'),
        )

If I create a smartgrid on the 'product' table using:
def product():
    return dict(grid=SQLFORM.smartgrid(
        db.product,
        linked_tables=['related_product'],
        ))

the "related_product" table appears twice because it references the
"product" table twice.  Any way to prevent this?

-Jim