plpy prepare problem

I'm having a bit of a problem getting plpython's prepare to work
properly:

CREATE OR REPLACE FUNCTION batch_item_reversal(b batch_item)
  RETURNS "varchar" AS
$BODY$

if b['reversal_flag'] == 'Y':
    sql = plpy.prepare("""
        SELECT batch_item_number
        FROM batch_item
        WHERE patient_ssn=$1 AND
            patient_dob=$1 AND
            claim_number=$1 AND
            batch_item_number != $1""",
        ["varchar", "date", "varchar", "varchar"])
    refs = plpy.execute(sql, [
        b['patient_ssn'],
        b['patient_dob'],
        b['claim_number'],
        b['batch_item_number']])

    refs2 = plpy.execute("""
        SELECT batch_item_number
        FROM batch_item
        WHERE patient_ssn='%s' AND
            patient_dob='%s' AND
            claim_number='%s' AND
            batch_item_number != '%s'
        """ % (b['patient_ssn'],
               b['patient_dob'],
                       b['claim_number'],
                       b['batch_item_number']))

    if refs:
        return refs[0]["batch_item_number"]
    else:
        return "ERROR"
else:
    return None

$BODY$
  LANGUAGE 'plpythonu' VOLATILE;


Here, refs2 returns the proper data, but refs always returns nothing.
I have a feeling it has something to do with the type list, I tried
all "text"'s but to no avail.