Since that intro is mine:

Something (or someOne!) is generating keyboard interrupts. I use standard gemdos calls for key input, so I really don't have a clue why this happens. Does this happen on specific games, or on some certain cases?

More than 5 test Falcons and 3 megastes (and 1 tt) never had any problems with this intro, and I haven't changed the code in about 2 years, so up till now I assumed it worked ok...