iPhoto identified faces never remembered

Hi,

For several years now, I hope that the next upgrade of iPhoto will fix a nagging bug with Faces. I am now running iPhoto 9.6 (latest on Yosemite).

Out of the thousands of pictures I have, there are about 20 pictures that no matter how many times I identify the people in them, iPhoto keeps prompting me to identify faces again.

Some photos are recent, some are very old and have gone through many upgrades of iPhoto. I just can't figure out why iPhoto can't remember my tagging the faces. Maybe there's something in the metadata, or the file size, or the file name, or something that throws iPhoto for a loop.

Either way, it's frustrating. I hope someone's find a workaround!