when you tried in MS-Dos+Quemu, did you run it through NC as well? (just for interest sake, since you meantioned it didn't happen there)
Even back in the days on a real machine, I tried not to run a game through NC, because I had some problems with it AFAIR.

Yes, I did. I always use a file manager when I do something in DOS. That's the reason why this bug appeared in DOSBox at all 😀