For the following, refer to vadracas's screenshot image several posts above.
There are a number of issues with those narrow (1 tile width) diagonal passages in the cave maps. While tight squeeze passages certainly are common in underground cavern systems and thus they fit the ambiance of the cave maps, the game engine just doesn't handle the diagonal ones well. I wonder if changing the diagonal path tiles and the filled tiles whose corners block line of sight through the passage such that a small gap appeared would be enough to resolve the problems with them. If not, then is it a requirement to have traversable tiles edge connected instead of only corner connected to each other? (Ignoring changing level up or down for simplicity of discussion)