Issue is that tag fails to get updated and is reverted to an original tag. However, now I've tried different search Views like "Albums" and it seem that it's working on ones that I've tried... Go figure.
This would bring a conclusion that it was "My Computer" view where tags would not 'not stick'.
I can reproduce in "My Computer" view in every case:
1. Select Disk#2 tracks
2. Tools->Scripts->Auto-Increment Track #s
3. Start numbering from '1'. Press OK. Wait until files are finished updating. I've waited as long as a few minutes.
4. Click on another folder, and then go back
5. Only few random files are updated.
That's still a 'nasty' bug as I almost 100% of the time am in 'My Computer' view to catalog new files. It's not always just music in these folders, it can be music and/or video, sometimes mixed therefore to see all files I must be in 'My Computer" to see all file types supported by MM4.