I'm helping my mother organize her photos in Windows Live Photo Gallery (Windows 7). We've been scanning in slides taken decades ago.
We want to arrange the photos by date, so we have been changing the "date taken" on the files. And that's where our troubles lie. To change the date, we right-click on the thumbnail and bring up the Properties. Then we enter the date the slide was taken; say, 10/16/1964. Click on OK and poof! the photo is gone. Just gone. It's not in the trash, it's not in some other folder. Perhaps it has been renamed, but I cannot find it anywhere.
I can reproduce this behavior on every photo we've been editing today. We've lost about a dozen just trying to figure out what's going on. (We have backups on the SD card the scanner uses.) Yesterday was a different matter. Oddly, it all worked perfectly yesterday. We haven't changed our process.
It's not just Windows Live Photo Gallery. Even Windows Explorer does it. Right-click on the image file, change any of the details (subject, tags, date, etc.), click OK and the file disappears.
Solved, but it's not pretty. You may be asking: what changed between yesterday and today. Answer: McAfee updated its virus definitions. We disabled real-time protection and everything returned to normal. Re-enable real-time protection and files start disappearing. Nice.
Another oddity: we went to empty the recycle bin. It said "are you sure you want to delete these 53 items?" (It contained images that we had trashed manually.) But the progress bar indicated it was actually deleting over 3,200 files. Hopefully McAfee hasn't randomly and silently deleted a bunch of other files.