You can't use the Parent > Child keyword notation when tagging faces -- LR will rename the child keyword to be a screwy name, and it can cause an internal error.
To reproduce:
1. Create two parent keywords, Friends and Family.
2. Under each of those keywords, create the child keywords Peter and assign each Peter to a separate photo. The hierarchy now looks like:
3. Go to a photo with no keywords, draw a face rectangle, and enter "Family > Peter" into the person box.
4. LR incorrectly renames the keyword Family > Peter to be Family > "Family > Peter":
Sometimes this can result in a LR internal error, "name is not unique", though I haven't been able to reproduce the exact steps for this to happen:
Is it expected behavior that a keyword named "Family > Peter" is created underneath Family? Or that an internal error sometimes occurs? Both seem like bugs.
Hmm, I think the renaming bit's a bug, and internal error's clearly not meant to happen. So yeah, I think you're right, reading back through the steps again.
______________________ The Lightroom Queen - Author of the Lightroom Missing FAQ & Edit Like a Pro books.
This arose when someone reported having two members of the family with the exact same first, middle, and last name (no Jr, Sr, or II). I have a number of people in my family with the exact same name, as well. There are two Ellis Ellis Ellises (yeah, New Englanders were sometimes quite strange).
While these relatively rare use cases can be worked around (e.g. with "Cousin" or "Uncle" or other annotations), it seemed natural to use the keyword hierarchy to resolve the ambiguity. (I first thought of that after reading your Whats New page, where you mention using the hierarchy for organization.)
I guess some hierarchies could get too long to show in the Faces field under the face itself. That's why I specifically mentioned making them unique in the blog post (or I hope I did.... I'll go running off to check!)
______________________ The Lightroom Queen - Author of the Lightroom Missing FAQ & Edit Like a Pro books.