With Game of Thrones for example I had to add this for every episode since they make extensive use of subtitle tracks when speaking Dothraki, Valyrian, etc. The 'd' flag was added automatically, but I had to manually add 'f' each time.
So I was just wondering why MakeMKV wouldn't automatically add the "f" flag when extracting any Forced Subtitle track and (as a paying user!

Thanks!