You load an MP3 for playback (in the etc. menu -> Play music) and want to hear it as you work on your quest file. When you save your work during the playback of an MP3, ZQ sometimes fails to save and then immediately crashes, losing your work. (However, the file that you were saving over is still safe)
EDIT: I played an MP3 file called "SleepSilentChild-qt3.mp3" which is found within the zip file of the quest "Death of Link" made by tlseward in PureZC. But does that occur on all MP3s?