I read, with interest, this correspondence from the Congregation for the Doctrine of the Faith. If I am understanding it correctly, when you convert to Mormonism, you can ask that your ancestors also be "posthumously baptized" so that you won't be lonely in heaven. Of course, since the Church of Latter Day Saints has basically abandoned the Gospel, there isn't much of a chance for salvation for the members of this church. I mean, it's not that everyone is damned. It's just so clear that salvation is much harder when your conception of God and Jesus Christ is screwed up. But, why should we care about what they do with baptismal records? They don't understand God. Why are we surprised that their conceptions of God's sacraments is wrong? And if that's wrong, nothing that they say or do matters, right?
I wonder if this has something to do with it. We believe that the you salvation is not entirely time dependent. In other words, it is possible to affect someone's eternal salvation after they have died. If a good catholic kid becomes an apostate to the Mormons, could that nullify the person's chance for salvation? I'm not sure. I think there may be a better reason but this sounded possible in my mind.