Rebirthed Sim "becoming" existing household member

I have done rebirth's successfully in the past (before the latest round of updates), but recently when I attempt to do a rebirth into a new household, instead of creating a new, separate sim and adding them to the household, it seems to overwrite one of the existing household members and turns that household sim INTO the rebirthed sim. It doesn't allow me to add a household member, it simply takes one of the existing household members and "rebirths" that household member, so when I press play, the rebirthed sim takes the place of the existing household member and uses that household members traits instead of that of the rebirthed sim's. I hope that makes sense.... If I try to rebirth a sim into a new household, with no existing members, it seems to work as it is supposed to, but if I rebirth the sim into an existing household, it doesn't work properly and simply replaces one of the household members. It will allow me to customize and edit the household member that has become the rebirthed sim, but then that household member disappears. Help!!