I thought it would be a good idea to collect the known LOS issues in one place, in case Kornel feels like tweaking the system. Not sure if that place is Bug Report or Feature Request :)
1) Firing around a corner with a shotgun behaves asymmetrically
2) sometimes the auto-aim ([f]) will select a path through a wall to shoot a visible target. you can generally work around this by aiming manually until you have a clear path.
3) not sure if this one is intentional:
You see : out of vision
You hear the scream of a freed soul!
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Rahul Armor : modified red armor [6/6] (84%) (P)
Health: 60% Exp: 3/53% Weapon: chaingun (1d6)x4 [24/40]
cautious Phobos Base Lev4
the former human killed to my northeast where the % is was able to shoot me, but I couldn't see him (you can see the corpse is still in the "dark")
examples of point #1 in the above image: the door to my southeast (around 4-5 spaces). standing immediately NE or NW of that and next to it, I cannot hit the wall 2 spaces to the south of the door by aiming at it with the combat shotgun, even though it is visible to me. I can stand SW/SE of the door and hit the wall 2 spaces to the north.
Feel free to add others, guys - I'm pretty sure there was at least one more oddity.