Some explored areas aren't visible when re-entering worlds.

[FLHerne]

Only the square region around the player is drawn when re-entering a world, with the rest filled as non-visible. If there are explored tiles outside that region, they're drawn as non-visible.

[FLHerne]

Even more conspicuous - some visible areas are still visible when travelling to portals near the departure point, even if they shouldn't be.
Less conspicuous - behaviour of fire and fuses at edge of visible region.
Same bug.

Redrawing only the area within the player's visible region is simply invalid now that significant visible changes can escape it.