It would be cool if the GOG version could somehow read the music off the disc, if you own it and put it in the drive. I wouldn't mind doing that if it meant better music performance ...

It's apparently a "WinMM" bug. I guess that's the reason why GOG is still unable to fix it.

I tried it now and I don't have any issues with music not repeating, but music does get aborted when accessing the menu. I also noticed something weird, seemingly a bug, but I don't know whether that's specific to the GOG version: The first boss shot me after I had hit him a few times, but when I reloaded my game and entered his room again, he went down with the first shot, as if the game had counted all the shots from the previous try and left him heavily wounded, even though I died and reloaded. I reloaded a few times to see if it was a coincidence but it was not. The savegame made him die with the first shot, no matter what distance I was away from him ...

EDIT: And now it also happened to me one time that the music stopped in-game and no new song was played. Maybe it just takes a while for that bug to appear, as it's not about repeating single songs but the whole playlist? So it's far from a perfect release. But still fun to play.