Savegame:
single_2.sv.zip
Pictures:

Vanilla bugs should be documented upstream
Because the function assumes only one tile can be wrong, it does not properly fix broken adjacent tiles.
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#.#
#.#
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If the second . had been a #, it would fix it. But instead it checks the second . to see if its a lava tile (it's not) and the fix fails.
Brought to you by yours truly:
// DRLG_L3PoolFix
if(dungeon[dunx + 1][duny] == 37) dungeon[dunx][duny] = 33;
if(dungeon[dunx + 1][duny] == 35) dungeon[dunx][duny] = 33;
@galaxyhaxz where exactly should the lines goe?
When I try to apply them there is still something not quite right about the level (notice the black spots in the lava)

Most helpful comment
Because the function assumes only one tile can be wrong, it does not properly fix broken adjacent tiles.
If the second
.had been a#, it would fix it. But instead it checks the second.to see if its a lava tile (it's not) and the fix fails.Brought to you by yours truly: