Above I've described the issue of the screen flashing the normal view of space at mission start, cutting to black, then fading in.
Opening & saving the first mission (attempted for purposes of dialog editing) in FRED, with no editing whatsoever done,
had the result of the screen going black & immediately fading in every 5 seconds, when I again tried to run the mission from Tech Room.
This did not, however, happen with the second mission, which showed exactly the expected old behavior.
Hidden Text: Reproduction efforts Show
The main difference in the sexp's responsible was the first mission fades in over 5000ms while the second uses 6500.
The event in question is called "initial-sequence" in mission 1, "fade-in" in mission 2. There's an event amb-music-play between them only in mission 2.
Setting the first mission to 6500 fixes this, although setting the arg of fade-in in the 2nd mission to 5000 does not reproduce the strange behavior there.
Merely renaming the offending event to "fade-in" in mission 1 fixes the issue too;
renaming to "initial-sequence" in mission 2 and reordering events to match 1 does not cause it.
I'm using nightly from 23Dec2020 self-built on Archlinux & forcing current MVPS.
FRED version is 21.0.0-RC2 in a Win7 VM.
My guess is that mission file 1 got corrupted in such a way that reading & writing it with a current FRED causes another event than was originally intended
to be written, unless the event itself is actually edited. Is this possible or even to be expected, considering the original file was last edited in 2009?
EDIT: Edit *anything at all* with the Events Editor and this bug doesn't show up.
I've simply removed the fade-out time at the beginning to instantly start with a black screen,
never touching the fade-in, and everything works.