Since some months ago we have been trying to hunt down some bug in my game. Basically, the invincibility theme got cut off early in gameplay, which hinted at a timing issue. The game was obviously taking up 1200 frames (20 seconds) as usual, so I wondered if the framerate system was failing on his (the musician's) system. First I reworked the framerate system so it literally stayed in sync with the timer instead of trying to count on its own, but that didn't work. I went as far as looking up hardware bugs (which I had assumed would be dead by now but I wanted to make sure) and trying to set the thread's affinity to avoid them. Nope.
...then I look at the OGG file again, just in case. It's 0.4 seconds longer than it should. Nobody noticed for months. *headdesk*