Select Union All. Mysql 4.1. Não junta os result set

ddata_lancamento
ffichas_encontradas
fvalor_informado
frelogio_mec_credito_atual
frelogio_mec_credito_anterior
frelogio_mec_premio_atual
frelogio_mec_premio_anterior
fvalor_ficha

select c.ddata_lancamento              as ddata_1,
       c.ffichas_encontradas           as ffichas_1,
       c.fvalor_informado              as fvalor_recebido_1,
       h.frelogio_mec_credito_atual    as frel_m_c_atual_1,
       h.frelogio_mec_credito_anterior as frel_m_c_anterior_1,
       h.frelogio_mec_premio_atual     as frel_m_p_atual_1,
       h.frelogio_mec_premio_anterior  as frel_m_p_anterior_1,
       h.fvalor_ficha                  as fvalor_ficha_1,
       cast(null as date)     as ddata_2,
       cast(null as unsigned) as ffichas_2,
       cast(null as unsigned) as fvalor_recebido_2,
       cast(null as unsigned) as frelogio_mec_credito_atual_2,
       cast(null as unsigned) as frelogio_mec_credito_anterior_2,
       cast(null as unsigned) as frelogio_mec_premio_atual_2,
       cast(null as unsigned) as frelogio_mec_premio_anterior_2,
       cast(null as unsigned) as fvalor_ficha_2
  from tb_maquinas_cobranca  c,
       tb_maquinas_historico h
 where c.nidentificador = h.nident_maquinas_cobrancas
union all
select cast(null as date)     as ddata_1,
       cast(null as unsigned) as ffichas_1,
       cast(null as unsigned) as fvalor_recebido_1,
       cast(null as unsigned) as frel_m_c_atual_1,
       cast(null as unsigned) as frel_m_c_anterior_1,
       cast(null as unsigned) as frel_m_p_atual_1,
       cast(null as unsigned) as frel_m_p_anterior_1,
       cast(null as unsigned) as fvalor_ficha_1,
       c.ddata_lancamento              as ddata_2,
       c.ffichas_encontradas           as ffichas_2,
       c.fvalor_informado              as fvalor_recebido_2,
       h.frelogio_mec_credito_atual    as frel_m_c_atual_2,
       h.frelogio_mec_credito_anterior as frel_m_c_anterior_2,
       h.frelogio_mec_premio_atual     as frel_m_p_atual_2,
       h.frelogio_mec_premio_anterior  as frel_m_p_anterior_2,
       h.fvalor_ficha                  as fvalor_ficha_2
  from tb_maquinas_cobranca  c,
       tb_maquinas_historico h
 where c.nidentificador = h.nident_maquinas_cobrancas