When (e.g.) I'm listening to an MP3 file, if I edit the comment (as displayed in the User Comment column), the edited comment appears correctly in the lister. But when the folder is refreshed or left and returned to, it turns out the edited comment wasn't saved, and the metadata was not updated. The MP3 had been opened by the player app, and was locked, but the lister showed a successful write.
I discovered this after working on several MP3 files, each in its own folder, and only when I was finished did I notice that none of the edited comments had actually been saved.
There should be some indication that the file was R/O and the metadata couldn't be written.