invisible line of sight obstruction observed in regional dump

[esotericist]

Describe the bug

while exploring the regional dump, i encountered an area that appeared to block line of sight without any physical presence explaining it.

Attach save file

note: this save is unlikely to be helpful as the problem cleared on save+load
East Lake-trimmed.tar.gz

Steps to reproduce

reproduction steps unclear. i experienced this exploring a regional dump, but i don't know that it's directly related to that.
the world had been explored for some time prior to this, the OMTs had long since been properly generated. but after moving around the vehicles in the screenshots below, i experienced an unexpected void.

Expected behavior

empty air should behave as empty air, and allow vision to pass through normally.

Screenshots

looking at z level 0:

looking at z level 1:

Versions and configuration

• OS: Linux
  • OS Version: Distributor ID: Ubuntu; Description: Ubuntu 24.04.1 LTS; Release: 24.04; Codename: noble;
• Game Version: cdda-experimental-2024-11-23-2130 98baf15 [64-bit]
• Graphics Version: Tiles
• Game Language: System language []
• Mods loaded: [
  Dark Days Ahead [dda],
  Disable NPC Needs [no_npc_food],
  Portal Storms Ignore NPCs [personal_portal_storms],
  Slowdown Fungal Growth [no_fungal_growth]
  ]

Additional context

No response

[PatrikLundell]

Failed to repeat the issue, as expected, unfortunately.
However, bringing up the debug terrain interface (debug menu-m-M) shows the same weird black outline at the level above, provided you haven't looked up. If you have looked up the debug edit menu shows the same restrictions as the normal view of the level above.
I didn't see anything odd in the edit data itself (although I'm not confident in my ability to interpret the data), as it seemed to suggest you have seen the air before and have visibility of it, as opposed to the "real" hidden air above the wreck, which is marked as not seen and with no visibility.

This suggest to me that it's a matter of a light/vision cache of some kind that isn't updated properly. However, I wouldn't expect these caches to be saved, but rather rebuilt on load, but maybe it is indeed saved, and only the current Z level rebuilt on load, leaving an erroneous Z+1 level cache behind.