Hi John,
Sorry to hear about this problem. I ran a quick test but was not able to reproduce the problem. This is what I did.
1. Put a CR2 on a flash drive
2. Edit that image in Nitro (on the flash drive). I turned it black and white.
3. Ejected the drive and inserted it into an iPad
4. Add the drive itself to Nitro.
5. Set the rating
6. Entered Edit – image was black and white.
Based on your description, the only thing I can think of is that the app was not able to read the XMP file (or couldn’t find it), so it made a new one.
I suggest re-running your test by editing on the Mac, and then going to iOS, but go into Edit first to see if the image’s edits appear. If they do, set the rating or flag. Does that work?