On zero TU tiles, I wrote a tool to report floors with 0 TU_Walk, and if it works correctly, there are 2 of them.
Two maps are affected:
ISLANDURBAN03.MAP posn (2,8,0)
ISLANDURBAN2.MCD:17 is a hill slope, not sure if should be used as a floor.
And many instances of FOREST.MCD:4 in SOLFOREST14.MAP.
This looks like a bug in FOREST.MCD:4 - its death tile is a burned floor one, LOFTs are ones for the floor, but all TU settings are 0.
This accounts for the bugged forest map, I've met this bug myself. What's up with the ratman village I don't know.