faces recently tagged...not tagged

I've been editing a large (500+) batch of photos, a hundred or so at a time in iPhoto. If I have to close iPhoto for some reason and then reopen it, the recently-face-identified photos no longer retain those identifications.

I am at my wits' end.

I am still on Mavericks. And yes, I'm still using iPhoto.

I have a lot of photos in my library (46,000) so sometimes things are a little slow.

But this has never happened to me before. I've tagged and re-tagged. But once again, when I opened iPhoto, my recently tagged photos no longer had faces identified.

Help.