Hey! Can you explain how does the impregnation occur and what you mean by "they aren't set to be able to"?
I took to male Sims, made sure they can only impregnate and not get pregnant, had woohoo that would cause pregnancy, but nothing came of it. I don't know how else I can test this, but this doesn't appear to be an issue on my side.
Still, I can see a possibility of this happening if somehow some kind of safeguards fail, so I will make sure to double check for it.