I couldn't help but notice that the swinging door had moved from its initial position within the corrupted sectorwork even though during play I had never gone anywhere near it to make it move.
So I investigated further.
First, at map start I immediately cheated my way over to the affected area to take a close look at the sectorwork:
So far, so good, right? Wrong. Something's about to hit the fan.
Then, I flew back to the museum's black sliding door, opened it, and then flew back to see if anything had changed.
In this screenshot, note that the swinging door has moved slightly.
After that, I flew back to the museum, opened the gray elevator door, and then flew back, and saw THIS:
Apparently, the sectorwork in the area of that swinging door is okay in the actual map file, but Went Very Wrong because the sliding doors in the museum interacted with it somehow. I think.
One other thing I noticed is that this corruption
doesn't happen consistently - I tested this multiple times and occasionally no such corruption would happen at all. (Is it because of doors being blocked or something when they try to move?)
By the way, the reason I asked what tools were used is because, unlike Mapster, other tools (like the original Build editor) don't have certain integrity checks and such, which can allow
really nasty shit to happen to maps without anyone noticing until it's too late.