I am just testing the map feature and painting on it within DISE. Doesn't look perfect yet but it's coming along! :) Actually, after testing a bit more, I'm not entirely convinced that DISE does it wrong after all. Here's why:

  1. Paint in DISE, then save.
  2. Restart DISE, then reload the game-save. Looks good! Just as I saved it.
  3. Load it in-game, then quit the game (which saves it).
  4. Load it in DISE. Looks just like it was in-game (with the errors).

The game was probably never meant to display explored areas like this, but I am slightly disappointed. :)