I had several images with faces, say person A and B. I wanted to change the tagged person A on one photo, so I changed the name to B. Now all the images with person A belong to person B, it looks like it merged the 2 persons. I think we should add a warning when changing one photo will affect several faces.
Workaround: press the eject button before changing a name: 
Side note: congrats that this new feature, this is great!
I had several images with faces, say person A and B. I wanted to change the tagged person A on one photo, so I changed the name to B. Now all the images with person A belong to person B, it looks like it merged the 2 persons. I think we should add a warning when changing one photo will affect several faces.
Workaround: press the eject button before changing a name:
Side note: congrats that this new feature, this is great!