Django ManyToManyField repeated values (that are the same object)

I'll try to sum up with a brief description of the logic. I have 2 models (I'm using django smart_selects too): One "actuacion" can be related with a previous actuacion and in that case they will have the same number of "parcelas" related.

from smart_selects.db_fields import ChainedForeignKey

class Actuacion(models.Model):
    [...]
    parcelas = models.ManyToManyField('Parcela', related_name="actuaciones", blank=True)
    actuacion_precedente = ChainedForeignKey(
        'self', on_delete=models.CASCADE, null=True, blank=True,
       chained_field="paraje", chained_model_field="paraje")

class Parcela(models.Model):
    [...]

In the admin I have:

class ActuacionAdmin(admin.ModelAdmin):
    [...]
    filter_horizontal = ('parcelas', )

After populating my database I take this output: (the first number is the ID of the object "parcela").

What the hell is going on? Reading directly the database gives me 5 objects properly. However the front-end is duplicating the information.

I've tested and played linking the first actuacion to a second one linked to a third one and the results appears thrice. (and with 4, 5... the same).

Any idea will be tested and appreciated.

Thanks for your help. Pablo :)