In Library Loupe view it's the most selected photos that your changes are applied to. So, make sure that you're working in Library 'Grid' view, not Loupe view.
Yup. I was in Grid view the whole time because I was trying to change metadata in multiple photos. But even when I selected only one photo from the grid view and went into "Edit Capture Date Time" sub-window with the selected photo's thumbnail showing in that sub-window, it still failed to change that photo's capture time and instead changed the capture time on a completely different file that wasn't even part of the original grid view and was not being displayed in the "Edit Capture Date and Time" sub-window!
The only thing that fixed it was shortening the file names so that the sequence numbers that differentiated them weren't so far away from the beginning of the file name. Just wondered if anyone knew what the "practical" LR limit was for length of filenames.
No, they are much shorter than 260 characters. As I mentioned in my original post, all of the file names were 39 characters long. But they all had the same 36-character string as a prefix, with the only differentiating characters being 3-digit sequence numbers in characters 37-38-39. They actually imported from the thumb-drive into LR and Windows 7 just fine. It was only when I tried to update their metadata that I ran into problems.
Try copying one of the files from the USB drive using Windows Explorer to your desktop. Import the file from your desktop into LR and see if you can now edit the capture time.
I copied all 58 photos from the USB drive to a folder on my C: drive. That all went fine so there is no issue with the length of the file path+names, or Windows would have barfed during the copy. In fact, I've discovered that the source of this problem is occurring during the Lightroom import and has nothing to do with file name length, although that initially appeared to be a factor. So technically, this thread should be shut down. But if you're interested in what I discovered... read on.
After I made the copies from USB drive to my hard drive (and before any Lightroom import), I was using the properties function from Windows Explorer to look at the "Taken Date and Time" for some of these photos. When viewed from Windows Explorer, they were ALL correct !!! This was the case on both the USB drive and the copies on my hard drive.
Then I went into Lightroom to import them from my hard drive. After setting up Imports from my hard drive several times, I discovered that Lightroom was shifting the "time taken" forward by 5 hours on different subsets of the 58 files each time I started an import. WEIRD!! Sometimes it would be just the last 5 photos, sometimes just the last 6. Other times the "time shifters" would be scattered in small groups throughout the 58 photo files. It seems to somewhat random as to how many and which photos get their time-taken shifted with each new import attempt.
If I go ahead and finish importing some of these "time shifters", they come into the catalog just fine (except for the wrong taken time). But if I immediately try to alter the "time taken" in the metadata, I get all the weird symptoms that I described in my original write up, such as adding an hour to the third photo actually adds an hour to the first photo, even though the first photo is not selected.. However, if I immediately exit LR after the import and then run it again, all the taken-times are still wrong, but the metadata updates work normally like you'd expect.
I have found some other threads about people getting their date taken shifted by x hours, sometimes even 5 hours exactly, but it's usually related to time zone settings in their cameras while they're traveling. Since my situation is random from one import to the next, and all these photos were taken at the same location in a two-hour span anyway, that's not the case here. But the photos weren't taken on my camera, and I don't know what that camera was putting into its metadata and EXIF data, etc.
So... I don't think this one is worth any more of our time! Thanks for your thoughts.