Hi Matias,
wwhich SPIS v4 do you use ? 4.0, 4.1 or 4.2 ?
4.1 and 4.3 can take account of multi species on a single emitter.
Perhaps you have found a bug related to this new capability. I suggest you to send me your project at mateo@onera.fr and I will look at it asap.
Regards,
Jean-Charles