Thanks for the feedback, Phil.
I am using Lightroom 3.4, but it doesn't work for me. I do see that for images that Lightroom tags, it does fill in the same field, which has me confused. Is it possible that something is masking Lightroom's reading of this field?
I tried it with another image with the same results, but I captured the exiftool output and diff'ed them.
This is before import into LR and after import into LR and adding a hierarchical subject:
6,7c6,7
< "File:FileSize": 57155,
< "File:FileModifyDate": "2011:07:29 16:34:58-07:00",
---
> "File:FileSize": 60207,
> "File:FileModifyDate": "2011:07:29 16:36:02-07:00",
10a11,12
> "File:ExifByteOrder": "MM",
> "File:CurrentIPTCDigest": "7299823d8f21d3283b54a517a7588a70",
21a24,34
> "EXIF:Orientation": 1,
> "EXIF:ExifVersion": "0221",
> "XMP:XMPToolkit": "Adobe XMP Core 5.2-c004 1.136881, 2010/06/10-18:11:35 ",
> "XMP:MetadataDate": "2011:07:29 16:36:02-07:00",
> "XMP:RawFileName": "q1.jpg",
> "XMP:HierarchicalSubject": "people|AAA",
> "XMP:Subject": ["AAA","people"],
> "IPTC:CodedCharacterSet": "\u001B%G",
> "IPTC:ApplicationRecordVersion": 4,
> "IPTC:Keywords": ["AAA","people"],
> "Photoshop:IPTCDigest": "7299823d8f21d3283b54a517a7588a70",
This is after adding the first subject and after adding a second subject:
6,7c6,7
< "File:FileSize": 60207,
< "File:FileModifyDate": "2011:07:29 16:36:02-07:00",
---
> "File:FileSize": 60284,
> "File:FileModifyDate": "2011:07:29 16:36:10-07:00",
12c12
< "File:CurrentIPTCDigest": "7299823d8f21d3283b54a517a7588a70",
---
> "File:CurrentIPTCDigest": "366c8ee4d52a05481d461677a04da172",
27c27
< "XMP:MetadataDate": "2011:07:29 16:36:02-07:00",
---
> "XMP:MetadataDate": "2011:07:29 16:36:10-07:00",
29,30c29,30
< "XMP:HierarchicalSubject": "people|AAA",
< "XMP:Subject": ["AAA","people"],
---
> "XMP:HierarchicalSubject": ["people|AAA","people|BBB"],
> "XMP:Subject": ["AAA","BBB","people"],
33,34c33,34
< "IPTC:Keywords": ["AAA","people"],
< "Photoshop:IPTCDigest": "7299823d8f21d3283b54a517a7588a70",
---
> "IPTC:Keywords": ["AAA","BBB","people"],
> "Photoshop:IPTCDigest": "366c8ee4d52a05481d461677a04da172",
If I take a clean file, add it to Lightroom, then using exiftool modify the HierarchicalSubject and MetadataDate tags, then reload the metadata into Lightroom, the subjects still don't show up. BUT, re-reading the tags from exiftool, I find that the HierarchicalSubject tag I entered has disappeared.
It seems like Lightroom is now using the digests to verify that it added the subjects, and if it didn't, removes them?

?