I have almost the same problem, tho mine is one of the waitress NPC's being mixed up with one of the maid NPC's. I could have my sim go to a restaurant and interact with the waitress NPC, it would be her face/name in his contacts list, but everytime he'd invite her over to his home, the maid would show up. She'd have the waitress's name and pic in his wants panel, even tho the maid looked nothing like her. I ended up killing the maid, then the waitress showed up for dates with no problem. This also happened in a prior install and i was surprised when it happened with this current install.
I don't mess around with SimPE (my phail at understanding SimPE, let me show you it) so i never use it.
Good to know I'm not alone. It doesn't seem to be causing any real problems, except the massive confusion that everyone's faces being mixed together brings, but then again, my disk copy of the game is about four years old.
*puts on her pirate hat* Disks? Where we're going, we don't need... disks.
Yeah, I don't know a whole lot about SimPE, but I use it anyway, which is why I bork on a regular basis. Oh well.