I think the key point to the issue is there is a difference between opening a BIAB file and importing it. Files dating back prior to 2007 will be midi plus the file extension type was different than now. There are also options the user may use to save with or without certain midi settings regarding patches. Even today, BIAB has an Import MGU option. Selecting that option and it appears BIAB is looking for odd extension files. I wasn't here back then and don't recall what those numbers mean but assume that system is likely causing the effect the user is experiencing.

Clues point to this being an archaic oddity and not a bug or problem.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Import MGU Option.jpg (115.21 KB, 25 downloads)
Import MGU Song.jpg (74.51 KB, 25 downloads)
Save with Patches and Harmony.jpg (17.53 KB, 25 downloads)

BIAB 2026:RB 2026, Latest builds: Dell Optiplex 7040 Desktop; Windows-10-64 bit, Intel Core i7-6700 3.4GHz CPU and 16 GB Ram Memory.