Reference Files (created in 2.50.2):
Quest With MIDI (1 slot loaded)
Quest With MIDI (2 slots loaded)
2.50.2, 2.50.3 RC1 & RC2.
2.53.0 B1 - B24, 2.55 Prelim 16 & 16.1 Expo Builds.
As of the switch away from the 2.50.3 RCs and toward the very first 2.53.0 beta, if you load a quest that has MIDI files in it, go to Quest -> Audio -> MIDIs to open the "Select Music" window, then exit that window either by clicking "Done" or pressing Esc, ZQuest will immediately crash.
I initially thought that maybe something went wrong while loading or editing the MIDI files in the 2.53 builds, but no, the files simply have to be in the quest, and all it takes to crash ZQuest is closing the "Select Music" window, even if you haven't done anything more than open it.
However, there are conditions.
First: it seems that 2 or more MIDI files need to be loaded for ZQuest to crash - which basically means that any quest by anybody wanting custom music will crash. When I load the reference quest with 2 MIDI slots, then open and close the "Select Music" window, this is the Windows dialogue I get:
And when I "click here," this is the further information provided:
Clicking again gives an absolutely massive text dump, which I can provide if necessary.
Now here's an odd variation: when I load the reference quest with 1 MIDI slot, then open and close the "Select Music" window, I only get visual glitches.
More than that, they vary depending on whether "Use Static for Invalid Data" is enabled.
With static disabled, ZQuest looks like this...
But wait, there's more!
Second condition: ZQuest only crashes if "Use Static for Invalid Data" is enabled.
With static disabled, quest files with 2 or more MIDIs loaded will only generate the Favorite Combos window removal glitch as noted above, instead of outright crashing. I confirmed using 2 different quests with over 20 and 40 MIDIs loaded, respectively.
And even more than that!
MIDI file size also seems to play into the equation. Loading a 100k MIDI file into slot 1 caused no problems, but loading a 3k MIDI file into the same slot caused the Favorite Combos window removal glitch.
This only happens in large mode. Small mode remains unaffected in all my tests so far.