JavLuv defers saving external nfo files in short bursts over time for reasons of performance. In some cases, I've made slight changes to the nfo file format, when I had to update all nfo files over time (like when I added support for Recently Added sorting). In other cases, the user might do bulk edits. In either case, this can require saving hundreds or even thousands of files, and take several minutes to save in total, if they were all done at once.
In your case, I'm betting you made a change, then closed JavLuv before the 10 second timer had a chance to detect the metadata had changed and saved the nfo file. It's maybe a bit unintuitive (I suppose I could kick off one last save job at exit), but it's technically not a bug. The next time you open JavLuv and wait at least 10 seconds, the nfo file would be saved.