Strange behaviour in continuous form - ms-access

Question

I have a table of employees with names and two surnames (in Spain two surnames are required).
To avoid erroneous entries, I have ONE surname table called "ST_JLE_Apellidos". In this way, what I store is the surname number, not the surname itself.
To feed the form I use the following SQL string (Where Table "Apellido2" is an instance of Table "Apellido1":
SELECT
JLE_Personal.Id_Personal_Personal,
JLE_Personal.Personal_NIF,
Apellido1.Personal_Apellido,
Apellido2.Personal_Apellido,
ST_JLE_Personal_Nombres.Personal_Nombre,
ST_JLE_CargosEnLaEmpresa.CargosEnLaEmpresa_CargoEnLaEmpresa,
ST_JLE_Municipios.Municipios_Municipio,
ST_JLE_Provincias.Provincias_Provincia,
ST_JLE_Paises.Paises_NombreCast,
JLE_Personal.Personal_Alta_FechaInicial,
JLE_Personal.Personal_Alta_FechaFinal
FROM
ST_JLE_Personal_Apellidos AS Apellido2
INNER JOIN (
ST_JLE_Personal_Apellidos AS Apellido1
INNER JOIN (
(
ST_JLE_Paises
INNER JOIN ST_JLE_Provincias ON ST_JLE_Paises.Id_Paises_Pais = ST_JLE_Provincias.Cod_Provincias_Pais
)
INNER JOIN (
ST_JLE_Municipios
INNER JOIN (
ST_JLE_CargosEnLaEmpresa
INNER JOIN (
ST_JLE_Personal_Nombres
INNER JOIN JLE_Personal ON ST_JLE_Personal_Nombres.Id_Personal_Nombre = JLE_Personal.Cod_Personal_Nombre
) ON ST_JLE_CargosEnLaEmpresa.Id_CargosEnLaEmpresa_CargoEnLaEmpresa = JLE_Personal.Cod_Personal_Cargo
) ON ST_JLE_Municipios.Id_Municipios_Municipio = JLE_Personal.Cod_Personal_Municipio
) ON ST_JLE_Provincias.Id_Provincias_Provincia = ST_JLE_Municipios.Cod_Municipios_Provincia
) ON Apellido1.Id_Personal_Apellido = JLE_Personal.Cod_Personal_Apellido1
) ON Apellido2.Id_Personal_Apellido = JLE_Personal.Cod_Personal_Apellido2;
Here is the MS-Access graphic window of the query:
And here is the result:
Everything correct so far.
The problem comes when I try to use a continuous form that contains the two last names:
TextBox 1: Apellido1.Personal_Apellido
TextBox 2: Apellido2.Personal_Apellido
MS-Access accepts both text boxes, but when I run the form, then Text Box 2 automatically changes to Apellido1.Personal_Apellido:
What could be the mistake that I am making?
Thanks in advance