Hey! By default, there are no TFB interactions, as WooHoo is merged with them, but assuming you kept them separate with a setting, WooHoo is just that, it doesn't cause pregnancy. In that situation, only TFB can cause pregnancy, but with a 0% chance it should have not happened so that's a mystery for now.
Of course, I have to mention, that other mods that alter pregnancy could have an effect, but I am not aware of any that do. At least not yet.
In any case, if this an issue, thank you for mentioning it, I will test things over again to be sure everything is in order. That's the best I can do in this situation.